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 $56.71   6.388%   $60.3326   $60.33   $60.35   $60.30  
  Purchase #2 $96.71   8.132%   $104.5745   $104.57   $104.55   $104.60  
  Purchase #3 $244.90   4.761%   $256.5597   $256.56   $256.55   $256.60  
  Purchase #4 $128.29   5.534%   $135.3896   $135.39   $135.40   $135.40  
  Purchase #5 $160.52   13.711%   $182.5289   $182.53   $182.55   $182.50  
  Purchase #6 $153.50   3.572%   $158.983   $158.98   $159.00   $159.00  
  Purchase #7 $170.54   9.159%   $186.1598   $186.16   $186.15   $186.20  
  7 purchase totals = $1,011.17       $1,084.5281   $1,084.52   $1,084.55   $1,084.60