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 $59.67   10.575%   $65.9801   $65.98   $66.00   $66.00  
  Purchase #2 $112.76   6.253%   $119.8109   $119.81   $119.80   $119.80  
  Purchase #3 $30.65   6.380%   $32.6055   $32.61   $32.60   $32.60  
  Purchase #4 $65.70   3.604%   $68.0678   $68.07   $68.05   $68.10  
  Purchase #5 $231.44   4.647%   $242.195   $242.20   $242.20   $242.20  
  Purchase #6 $145.31   13.516%   $164.9501   $164.95   $164.95   $165.00  
  Purchase #7 $34.65   8.228%   $37.501   $37.50   $37.50   $37.50  
  7 purchase totals = $680.18       $731.1104   $731.12   $731.10   $731.20