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 $59.71   6.207%   $63.4162   $63.42   $63.40   $63.40  
  Purchase #2 $11.43   7.241%   $12.2576   $12.26   $12.25   $12.30  
  Purchase #3 $192.60   3.832%   $199.9804   $199.98   $200.00   $200.00  
  Purchase #4 $226.38   3.775%   $234.9258   $234.93   $234.95   $234.90  
  Purchase #5 $31.54   4.751%   $33.0385   $33.04   $33.05   $33.00  
  Purchase #6 $45.27   7.778%   $48.7911   $48.79   $48.80   $48.80  
  Purchase #7 $115.69   5.369%   $121.9014   $121.90   $121.90   $121.90  
  7 purchase totals = $682.62       $714.3110   $714.32   $714.35   $714.30