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 $153.84   4.659%   $161.0074   $161.01   $161.00   $161.00  
  Purchase #2 $195.95   9.594%   $214.7494   $214.75   $214.75   $214.70  
  Purchase #3 $153.27   12.156%   $171.9015   $171.90   $171.90   $171.90  
  Purchase #4 $17.88   7.663%   $19.2501   $19.25   $19.25   $19.30  
  Purchase #5 $236.67   10.227%   $260.8742   $260.87   $260.85   $260.90  
  Purchase #6 $116.39   11.638%   $129.9355   $129.94   $129.95   $129.90  
  Purchase #7 $87.32   5.808%   $92.3915   $92.39   $92.40   $92.40  
  7 purchase totals = $961.32       $1,050.1096   $1,050.11   $1,050.10   $1,050.10