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 $55.79   6.274%   $59.2903   $59.29   $59.30   $59.30  
  Purchase #2 $93.46   4.125%   $97.3152   $97.32   $97.30   $97.30  
  Purchase #3 $17.67   6.772%   $18.8666   $18.87   $18.85   $18.90  
  Purchase #4 $81.81   13.264%   $92.6613   $92.66   $92.65   $92.70  
  Purchase #5 $206.75   12.785%   $233.183   $233.18   $233.20   $233.20  
  Purchase #6 $85.60   8.132%   $92.561   $92.56   $92.55   $92.60  
  Purchase #7 $198.28   4.793%   $207.7836   $207.78   $207.80   $207.80  
  7 purchase totals = $739.36       $801.6610   $801.66   $801.65   $801.80