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 $55.25   12.241%   $62.0132   $62.01   $62.00   $62.00  
  Purchase #2 $241.66   10.652%   $267.4016   $267.40   $267.40   $267.40  
  Purchase #3 $33.47   12.199%   $37.553   $37.55   $37.55   $37.60  
  Purchase #4 $59.62   13.738%   $67.8106   $67.81   $67.80   $67.80  
  Purchase #5 $157.26   3.354%   $162.5345   $162.53   $162.55   $162.50  
  Purchase #6 $83.50   11.406%   $93.024   $93.02   $93.00   $93.00  
  Purchase #7 $204.25   3.345%   $211.0822   $211.08   $211.10   $211.10  
  7 purchase totals = $835.01       $901.4191   $901.40   $901.40   $901.40