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 $234.95   6.848%   $251.0394   $251.04   $251.05   $251.00  
  Purchase #2 $132.97   8.568%   $144.3629   $144.36   $144.35   $144.40  
  Purchase #3 $140.39   13.707%   $159.6333   $159.63   $159.65   $159.60  
  Purchase #4 $158.40   10.171%   $174.5109   $174.51   $174.50   $174.50  
  Purchase #5 $236.94   6.292%   $251.8483   $251.85   $251.85   $251.80  
  Purchase #6 $118.64   4.356%   $123.808   $123.81   $123.80   $123.80  
  Purchase #7 $90.76   7.343%   $97.4245   $97.42   $97.40   $97.40  
  7 purchase totals = $1,113.05       $1,202.6273   $1,202.62   $1,202.60   $1,202.50