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 $65.83   11.424%   $73.3504   $73.35   $73.35   $73.40  
  Purchase #2 $166.66   9.285%   $182.1344   $182.13   $182.15   $182.10  
  Purchase #3 $119.88   13.671%   $136.2688   $136.27   $136.25   $136.30  
  Purchase #4 $237.64   9.298%   $259.7358   $259.74   $259.75   $259.70  
  Purchase #5 $39.82   4.279%   $41.5239   $41.52   $41.50   $41.50  
  Purchase #6 $67.56   6.169%   $71.7278   $71.73   $71.75   $71.70  
  Purchase #7 $36.55   12.230%   $41.0201   $41.02   $41.00   $41.00  
  7 purchase totals = $733.94       $805.7612   $805.76   $805.75   $805.70