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 $60.79   13.434%   $68.9565   $68.96   $68.95   $69.00  
  Purchase #2 $8.75   11.733%   $9.7766   $9.78   $9.80   $9.80  
  Purchase #3 $248.49   11.584%   $277.2751   $277.28   $277.30   $277.30  
  Purchase #4 $128.52   4.209%   $133.9294   $133.93   $133.95   $133.90  
  Purchase #5 $225.26   13.734%   $256.1972   $256.20   $256.20   $256.20  
  Purchase #6 $159.32   4.278%   $166.1357   $166.14   $166.15   $166.10  
  Purchase #7 $168.41   8.196%   $182.2129   $182.21   $182.20   $182.20  
  7 purchase totals = $999.54       $1,094.4834   $1,094.50   $1,094.55   $1,094.50