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 $244.70   11.470%   $272.7671   $272.77   $272.75   $272.80  
  Purchase #2 $22.61   7.817%   $24.3774   $24.38   $24.40   $24.40  
  Purchase #3 $117.45   9.367%   $128.4515   $128.45   $128.45   $128.50  
  Purchase #4 $136.52   5.572%   $144.1269   $144.13   $144.15   $144.10  
  Purchase #5 $170.89   12.313%   $191.9317   $191.93   $191.95   $191.90  
  Purchase #6 $40.51   13.547%   $45.9979   $46.00   $46.00   $46.00  
  Purchase #7 $181.67   8.586%   $197.2682   $197.27   $197.25   $197.30  
  7 purchase totals = $914.35       $1,004.9207   $1,004.93   $1,004.95   $1,005.00