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 $56.27   11.433%   $62.7033   $62.70   $62.70   $62.70  
  Purchase #2 $230.33   3.399%   $238.1589   $238.16   $238.15   $238.20  
  Purchase #3 $91.44   8.438%   $99.1557   $99.16   $99.15   $99.20  
  Purchase #4 $160.96   5.846%   $170.3697   $170.37   $170.35   $170.40  
  Purchase #5 $98.41   6.451%   $104.7584   $104.76   $104.75   $104.80  
  Purchase #6 $202.87   5.773%   $214.5817   $214.58   $214.60   $214.60  
  Purchase #7 $57.95   11.507%   $64.6183   $64.62   $64.60   $64.60  
  7 purchase totals = $898.23       $954.3460   $954.35   $954.30   $954.50