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 $214.36   6.341%   $227.9526   $227.95   $227.95   $228.00  
  Purchase #2 $27.25   6.224%   $28.946   $28.95   $28.95   $28.90  
  Purchase #3 $44.79   4.803%   $46.9413   $46.94   $46.95   $46.90  
  Purchase #4 $31.42   5.871%   $33.2647   $33.26   $33.25   $33.30  
  Purchase #5 $236.99   9.621%   $259.7908   $259.79   $259.80   $259.80  
  Purchase #6 $56.34   4.498%   $58.8742   $58.87   $58.85   $58.90  
  Purchase #7 $98.31   3.561%   $101.8108   $101.81   $101.80   $101.80  
  7 purchase totals = $709.46       $757.5804   $757.57   $757.55   $757.60