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 $90.90   3.641%   $94.2097   $94.21   $94.20   $94.20  
  Purchase #2 $250.92   4.665%   $262.6254   $262.63   $262.65   $262.60  
  Purchase #3 $89.32   7.115%   $95.6751   $95.68   $95.70   $95.70  
  Purchase #4 $197.48   11.436%   $220.0638   $220.06   $220.05   $220.10  
  Purchase #5 $103.61   10.496%   $114.4849   $114.48   $114.50   $114.50  
  Purchase #6 $211.64   8.265%   $229.132   $229.13   $229.15   $229.10  
  Purchase #7 $23.53   8.403%   $25.5072   $25.51   $25.50   $25.50  
  7 purchase totals = $967.40       $1,041.6981   $1,041.70   $1,041.75   $1,041.70