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 $44.86   11.565%   $50.0481   $50.05   $50.05   $50.00  
  Purchase #2 $231.56   13.214%   $262.1583   $262.16   $262.15   $262.20  
  Purchase #3 $202.45   12.284%   $227.319   $227.32   $227.30   $227.30  
  Purchase #4 $102.46   3.560%   $106.1076   $106.11   $106.10   $106.10  
  Purchase #5 $232.60   4.457%   $242.967   $242.97   $242.95   $243.00  
  Purchase #6 $144.66   9.713%   $158.7108   $158.71   $158.70   $158.70  
  Purchase #7 $210.63   11.468%   $234.785   $234.79   $234.80   $234.80  
  7 purchase totals = $1,169.22       $1,282.0958   $1,282.11   $1,282.05   $1,282.10