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 $53.46   12.377%   $60.0767   $60.08   $60.10   $60.10  
  Purchase #2 $208.54   5.455%   $219.9159   $219.92   $219.90   $219.90  
  Purchase #3 $6.38   4.445%   $6.6636   $6.66   $6.65   $6.70  
  Purchase #4 $250.34   8.623%   $271.9268   $271.93   $271.95   $271.90  
  Purchase #5 $65.79   11.759%   $73.5262   $73.53   $73.55   $73.50  
  Purchase #6 $58.60   13.628%   $66.586   $66.59   $66.60   $66.60  
  Purchase #7 $92.57   3.774%   $96.0636   $96.06   $96.05   $96.10  
  7 purchase totals = $735.68       $794.7588   $794.77   $794.80   $794.80