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 $226.28   12.695%   $255.0062   $255.01   $255.00   $255.00  
  Purchase #2 $229.27   3.128%   $236.4416   $236.44   $236.45   $236.40  
  Purchase #3 $157.68   3.393%   $163.0301   $163.03   $163.05   $163.00  
  Purchase #4 $157.26   8.805%   $171.1067   $171.11   $171.10   $171.10  
  Purchase #5 $56.30   5.817%   $59.575   $59.58   $59.60   $59.60  
  Purchase #6 $187.31   9.618%   $205.3255   $205.33   $205.35   $205.30  
  Purchase #7 $182.96   6.747%   $195.3043   $195.30   $195.30   $195.30  
  7 purchase totals = $1,197.06       $1,285.7894   $1,285.80   $1,285.85   $1,285.70