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 $58.98   13.533%   $66.9618   $66.96   $66.95   $67.00  
  Purchase #2 $199.60   9.607%   $218.7756   $218.78   $218.80   $218.80  
  Purchase #3 $248.90   10.717%   $275.5746   $275.57   $275.55   $275.60  
  Purchase #4 $46.80   11.211%   $52.0467   $52.05   $52.05   $52.00  
  Purchase #5 $133.96   5.612%   $141.4778   $141.48   $141.50   $141.50  
  Purchase #6 $128.77   11.610%   $143.7202   $143.72   $143.70   $143.70  
  Purchase #7 $25.89   12.848%   $29.2163   $29.22   $29.20   $29.20  
  7 purchase totals = $842.90       $927.7730   $927.78   $927.75   $927.80