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 $142.72   7.568%   $153.521   $153.52   $153.50   $153.50  
  Purchase #2 $72.27   3.434%   $74.7518   $74.75   $74.75   $74.80  
  Purchase #3 $115.86   8.438%   $125.6363   $125.64   $125.65   $125.60  
  Purchase #4 $190.54   9.111%   $207.9001   $207.90   $207.90   $207.90  
  Purchase #5 $155.70   10.572%   $172.1606   $172.16   $172.15   $172.20  
  Purchase #6 $110.75   5.786%   $117.158   $117.16   $117.15   $117.20  
  Purchase #7 $219.41   11.662%   $244.9976   $245.00   $245.00   $245.00  
  7 purchase totals = $1,007.25       $1,096.1254   $1,096.13   $1,096.10   $1,096.20