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 $208.72   8.781%   $227.0477   $227.05   $227.05   $227.00  
  Purchase #2 $44.51   8.612%   $48.3432   $48.34   $48.35   $48.30  
  Purchase #3 $124.39   4.845%   $130.4167   $130.42   $130.40   $130.40  
  Purchase #4 $209.45   8.869%   $228.0261   $228.03   $228.05   $228.00  
  Purchase #5 $83.66   10.532%   $92.4711   $92.47   $92.45   $92.50  
  Purchase #6 $74.27   7.612%   $79.9234   $79.92   $79.90   $79.90  
  Purchase #7 $208.63   10.596%   $230.7364   $230.74   $230.75   $230.70  
  7 purchase totals = $953.63       $1,036.9646   $1,036.97   $1,036.95   $1,036.80