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 $41.44   12.456%   $46.6018   $46.60   $46.60   $46.60  
  Purchase #2 $204.73   10.505%   $226.2369   $226.24   $226.25   $226.20  
  Purchase #3 $63.81   9.167%   $69.6595   $69.66   $69.65   $69.70  
  Purchase #4 $26.39   13.717%   $30.0099   $30.01   $30.00   $30.00  
  Purchase #5 $221.58   10.264%   $244.323   $244.32   $244.30   $244.30  
  Purchase #6 $39.26   13.691%   $44.6351   $44.64   $44.65   $44.60  
  Purchase #7 $194.98   3.781%   $202.3522   $202.35   $202.35   $202.40  
  7 purchase totals = $792.19       $863.8184   $863.82   $863.80   $863.80