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 $83.27   12.139%   $93.3781   $93.38   $93.40   $93.40  
  Purchase #2 $169.71   6.160%   $180.1641   $180.16   $180.15   $180.20  
  Purchase #3 $7.30   5.852%   $7.7272   $7.73   $7.75   $7.70  
  Purchase #4 $167.66   8.757%   $182.342   $182.34   $182.35   $182.30  
  Purchase #5 $203.83   3.283%   $210.5217   $210.52   $210.50   $210.50  
  Purchase #6 $226.83   12.666%   $255.5603   $255.56   $255.55   $255.60  
  Purchase #7 $250.75   6.130%   $266.121   $266.12   $266.10   $266.10  
  7 purchase totals = $1,109.35       $1,195.8144   $1,195.81   $1,195.80   $1,195.80