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 $95.53   6.519%   $101.7576   $101.76   $101.75   $101.80  
  Purchase #2 $93.25   9.409%   $102.0239   $102.02   $102.00   $102.00  
  Purchase #3 $74.68   9.841%   $82.0293   $82.03   $82.05   $82.00  
  Purchase #4 $47.26   6.828%   $50.4869   $50.49   $50.50   $50.50  
  Purchase #5 $242.48   13.215%   $274.5237   $274.52   $274.50   $274.50  
  Purchase #6 $146.82   13.819%   $167.1091   $167.11   $167.10   $167.10  
  Purchase #7 $98.26   7.200%   $105.3347   $105.33   $105.35   $105.30  
  7 purchase totals = $798.28       $883.2652   $883.26   $883.25   $883.20