Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $160.90   9.392%   $176.0117   $176.01   $176.00   $176.00  
  Purchase #2 $150.78   12.314%   $169.347   $169.35   $169.35   $169.30  
  Purchase #3 $220.85   10.471%   $243.9752   $243.98   $244.00   $244.00  
  Purchase #4 $184.53   13.869%   $210.1225   $210.12   $210.10   $210.10  
  Purchase #5 $204.53   11.203%   $227.4435   $227.44   $227.45   $227.40  
  Purchase #6 $128.49   13.465%   $145.7912   $145.79   $145.80   $145.80  
  Purchase #7 $113.72   7.794%   $122.5833   $122.58   $122.60   $122.60  
  7 purchase totals = $1,163.80       $1,295.2744   $1,295.27   $1,295.30   $1,295.20