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 $14.37   10.827%   $15.9258   $15.93   $15.95   $15.90  
  Purchase #2 $180.62   7.214%   $193.6499   $193.65   $193.65   $193.60  
  Purchase #3 $216.42   6.205%   $229.8489   $229.85   $229.85   $229.80  
  Purchase #4 $94.93   6.697%   $101.2875   $101.29   $101.30   $101.30  
  Purchase #5 $46.72   5.325%   $49.2078   $49.21   $49.20   $49.20  
  Purchase #6 $164.68   6.676%   $175.674   $175.67   $175.65   $175.70  
  Purchase #7 $80.39   9.871%   $88.3253   $88.33   $88.35   $88.30  
  7 purchase totals = $798.13       $853.9192   $853.93   $853.95   $853.80