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 $45.51   7.652%   $48.9924   $48.99   $49.00   $49.00  
  Purchase #2 $25.96   3.193%   $26.7889   $26.79   $26.80   $26.80  
  Purchase #3 $234.82   5.173%   $246.9672   $246.97   $246.95   $247.00  
  Purchase #4 $166.76   5.409%   $175.78   $175.78   $175.80   $175.80  
  Purchase #5 $119.34   8.425%   $129.3944   $129.39   $129.40   $129.40  
  Purchase #6 $13.27   13.421%   $15.051   $15.05   $15.05   $15.10  
  Purchase #7 $191.27   9.595%   $209.6224   $209.62   $209.60   $209.60  
  7 purchase totals = $796.93       $852.5963   $852.59   $852.60   $852.70