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 $6.28   11.521%   $7.0035   $7.00   $7.00   $7.00  
  Purchase #2 $94.43   4.793%   $98.956   $98.96   $98.95   $99.00  
  Purchase #3 $89.44   4.837%   $93.7662   $93.77   $93.75   $93.80  
  Purchase #4 $187.27   8.181%   $202.5906   $202.59   $202.60   $202.60  
  Purchase #5 $249.59   13.753%   $283.9161   $283.92   $283.90   $283.90  
  Purchase #6 $182.55   6.847%   $195.0492   $195.05   $195.05   $195.00  
  Purchase #7 $71.66   4.726%   $75.0467   $75.05   $75.05   $75.00  
  7 purchase totals = $881.22       $956.3283   $956.34   $956.30   $956.30