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 $40.95   8.128%   $44.2784   $44.28   $44.30   $44.30  
  Purchase #2 $88.94   6.514%   $94.7336   $94.73   $94.75   $94.70  
  Purchase #3 $202.73   8.835%   $220.6412   $220.64   $220.65   $220.60  
  Purchase #4 $174.29   9.198%   $190.3212   $190.32   $190.30   $190.30  
  Purchase #5 $60.91   8.726%   $66.225   $66.23   $66.25   $66.20  
  Purchase #6 $231.89   13.630%   $263.4966   $263.50   $263.50   $263.50  
  Purchase #7 $69.57   10.366%   $76.7816   $76.78   $76.80   $76.80  
  7 purchase totals = $869.28       $956.4776   $956.48   $956.55   $956.40