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 $58.79   4.275%   $61.3033   $61.30   $61.30   $61.30  
  Purchase #2 $177.84   7.227%   $190.6925   $190.69   $190.70   $190.70  
  Purchase #3 $99.66   3.125%   $102.7744   $102.77   $102.75   $102.80  
  Purchase #4 $24.27   12.246%   $27.2421   $27.24   $27.25   $27.20  
  Purchase #5 $249.64   4.293%   $260.357   $260.36   $260.35   $260.40  
  Purchase #6 $9.87   13.273%   $11.18   $11.18   $11.20   $11.20  
  Purchase #7 $172.76   4.208%   $180.0297   $180.03   $180.05   $180.00  
  7 purchase totals = $792.83       $833.5790   $833.57   $833.60   $833.60