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 $90.71   4.435%   $94.733   $94.73   $94.75   $94.70  
  Purchase #2 $10.96   8.262%   $11.8655   $11.87   $11.85   $11.90  
  Purchase #3 $14.75   11.507%   $16.4473   $16.45   $16.45   $16.40  
  Purchase #4 $201.65   9.310%   $220.4236   $220.42   $220.40   $220.40  
  Purchase #5 $127.48   5.413%   $134.3805   $134.38   $134.40   $134.40  
  Purchase #6 $43.64   8.642%   $47.4114   $47.41   $47.40   $47.40  
  Purchase #7 $139.49   12.464%   $156.876   $156.88   $156.90   $156.90  
  7 purchase totals = $628.68       $682.1373   $682.14   $682.15   $682.10