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 $65.51   3.812%   $68.0072   $68.01   $68.00   $68.00  
  Purchase #2 $116.89   10.475%   $129.1342   $129.13   $129.15   $129.10  
  Purchase #3 $19.50   11.248%   $21.6934   $21.69   $21.70   $21.70  
  Purchase #4 $82.97   7.239%   $88.9762   $88.98   $89.00   $89.00  
  Purchase #5 $229.30   3.531%   $237.3966   $237.40   $237.40   $237.40  
  Purchase #6 $248.89   5.499%   $262.5765   $262.58   $262.60   $262.60  
  Purchase #7 $178.88   13.481%   $202.9948   $202.99   $203.00   $203.00  
  7 purchase totals = $941.94       $1,010.7789   $1,010.78   $1,010.85   $1,010.80