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 $233.73   4.223%   $243.6004   $243.60   $243.60   $243.60  
  Purchase #2 $94.87   7.690%   $102.1655   $102.17   $102.15   $102.20  
  Purchase #3 $74.28   9.224%   $81.1316   $81.13   $81.15   $81.10  
  Purchase #4 $119.86   12.375%   $134.6927   $134.69   $134.70   $134.70  
  Purchase #5 $94.57   4.487%   $98.8134   $98.81   $98.80   $98.80  
  Purchase #6 $60.27   9.411%   $65.942   $65.94   $65.95   $65.90  
  Purchase #7 $183.96   8.166%   $198.9822   $198.98   $199.00   $199.00  
  7 purchase totals = $861.54       $925.3278   $925.32   $925.35   $925.30