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 $94.93   9.407%   $103.8601   $103.86   $103.85   $103.90  
  Purchase #2 $216.61   11.236%   $240.9483   $240.95   $240.95   $240.90  
  Purchase #3 $118.91   7.104%   $127.3574   $127.36   $127.35   $127.40  
  Purchase #4 $49.73   8.292%   $53.8536   $53.85   $53.85   $53.90  
  Purchase #5 $53.26   9.564%   $58.3538   $58.35   $58.35   $58.40  
  Purchase #6 $72.78   12.200%   $81.6592   $81.66   $81.65   $81.70  
  Purchase #7 $242.89   7.375%   $260.8031   $260.80   $260.80   $260.80  
  7 purchase totals = $849.11       $926.8355   $926.83   $926.80   $927.00