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 $151.41   11.750%   $169.2007   $169.20   $169.20   $169.20  
  Purchase #2 $176.84   12.767%   $199.4172   $199.42   $199.40   $199.40  
  Purchase #3 $243.63   8.602%   $264.5871   $264.59   $264.60   $264.60  
  Purchase #4 $239.60   7.502%   $257.5748   $257.57   $257.55   $257.60  
  Purchase #5 $154.26   3.867%   $160.2252   $160.23   $160.25   $160.20  
  Purchase #6 $208.76   11.220%   $232.1829   $232.18   $232.20   $232.20  
  Purchase #7 $59.93   7.593%   $64.4805   $64.48   $64.50   $64.50  
  7 purchase totals = $1,234.43       $1,347.6684   $1,347.67   $1,347.70   $1,347.70