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 $26.62   11.808%   $29.7633   $29.76   $29.75   $29.80  
  Purchase #2 $95.42   11.265%   $106.1691   $106.17   $106.15   $106.20  
  Purchase #3 $74.37   4.868%   $77.9903   $77.99   $78.00   $78.00  
  Purchase #4 $185.46   9.633%   $203.3254   $203.33   $203.35   $203.30  
  Purchase #5 $97.96   10.616%   $108.3594   $108.36   $108.35   $108.40  
  Purchase #6 $122.33   11.728%   $136.6769   $136.68   $136.70   $136.70  
  Purchase #7 $124.91   4.592%   $130.6459   $130.65   $130.65   $130.60  
  7 purchase totals = $727.07       $792.9303   $792.94   $792.95   $793.00