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 $86.68   12.519%   $97.5315   $97.53   $97.55   $97.50  
  Purchase #2 $141.49   12.196%   $158.7461   $158.75   $158.75   $158.70  
  Purchase #3 $147.56   9.779%   $161.9899   $161.99   $162.00   $162.00  
  Purchase #4 $25.32   9.298%   $27.6743   $27.67   $27.65   $27.70  
  Purchase #5 $138.34   12.417%   $155.5177   $155.52   $155.50   $155.50  
  Purchase #6 $100.41   11.783%   $112.2413   $112.24   $112.25   $112.20  
  Purchase #7 $59.64   13.740%   $67.8345   $67.83   $67.85   $67.80  
  7 purchase totals = $699.44       $781.5353   $781.53   $781.55   $781.40