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 $49.26   13.601%   $55.9599   $55.96   $55.95   $56.00  
  Purchase #2 $91.59   7.393%   $98.3612   $98.36   $98.35   $98.40  
  Purchase #3 $72.49   5.577%   $76.5328   $76.53   $76.55   $76.50  
  Purchase #4 $127.52   5.664%   $134.7427   $134.74   $134.75   $134.70  
  Purchase #5 $144.65   8.385%   $156.7789   $156.78   $156.80   $156.80  
  Purchase #6 $146.50   3.288%   $151.3169   $151.32   $151.30   $151.30  
  Purchase #7 $101.43   11.723%   $113.3206   $113.32   $113.30   $113.30  
  7 purchase totals = $733.44       $787.0130   $787.01   $787.00   $787.00