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 $236.88   7.565%   $254.8   $254.80   $254.80   $254.80  
  Purchase #2 $91.80   3.392%   $94.9139   $94.91   $94.90   $94.90  
  Purchase #3 $30.29   10.298%   $33.4093   $33.41   $33.40   $33.40  
  Purchase #4 $149.27   5.579%   $157.5978   $157.60   $157.60   $157.60  
  Purchase #5 $36.29   10.581%   $40.1298   $40.13   $40.15   $40.10  
  Purchase #6 $176.56   7.118%   $189.1275   $189.13   $189.15   $189.10  
  Purchase #7 $20.33   11.277%   $22.6226   $22.62   $22.60   $22.60  
  7 purchase totals = $741.42       $792.6009   $792.60   $792.60   $792.50