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 $84.77   12.433%   $95.3095   $95.31   $95.30   $95.30  
  Purchase #2 $66.33   7.312%   $71.18   $71.18   $71.20   $71.20  
  Purchase #3 $99.30   4.369%   $103.6384   $103.64   $103.65   $103.60  
  Purchase #4 $97.82   13.104%   $110.6383   $110.64   $110.65   $110.60  
  Purchase #5 $13.36   11.790%   $14.9351   $14.94   $14.95   $14.90  
  Purchase #6 $248.61   10.463%   $274.6221   $274.62   $274.60   $274.60  
  Purchase #7 $32.89   10.802%   $36.4428   $36.44   $36.45   $36.40  
  7 purchase totals = $643.08       $706.7662   $706.77   $706.80   $706.60