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 $84.65   13.515%   $96.0904   $96.09   $96.10   $96.10  
  Purchase #2 $209.55   7.412%   $225.0818   $225.08   $225.10   $225.10  
  Purchase #3 $136.32   3.272%   $140.7804   $140.78   $140.80   $140.80  
  Purchase #4 $135.49   12.468%   $152.3829   $152.38   $152.40   $152.40  
  Purchase #5 $9.92   10.161%   $10.928   $10.93   $10.95   $10.90  
  Purchase #6 $237.72   10.472%   $262.614   $262.61   $262.60   $262.60  
  Purchase #7 $110.75   4.159%   $115.3561   $115.36   $115.35   $115.40  
  7 purchase totals = $924.40       $1,003.2336   $1,003.23   $1,003.30   $1,003.30