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 $83.28   10.772%   $92.2509   $92.25   $92.25   $92.30  
  Purchase #2 $195.98   12.241%   $219.9699   $219.97   $219.95   $220.00  
  Purchase #3 $151.35   4.221%   $157.7385   $157.74   $157.75   $157.70  
  Purchase #4 $54.43   9.514%   $59.6085   $59.61   $59.60   $59.60  
  Purchase #5 $41.81   6.810%   $44.6573   $44.66   $44.65   $44.70  
  Purchase #6 $98.43   13.760%   $111.974   $111.97   $111.95   $112.00  
  Purchase #7 $183.78   11.320%   $204.5839   $204.58   $204.60   $204.60  
  7 purchase totals = $809.06       $890.7830   $890.78   $890.75   $890.90