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 $107.35   10.601%   $118.7302   $118.73   $118.75   $118.70  
  Purchase #2 $168.38   4.385%   $175.7635   $175.76   $175.75   $175.80  
  Purchase #3 $222.29   6.403%   $236.5232   $236.52   $236.50   $236.50  
  Purchase #4 $62.88   6.449%   $66.9351   $66.94   $66.95   $66.90  
  Purchase #5 $39.90   11.640%   $44.5444   $44.54   $44.55   $44.50  
  Purchase #6 $177.54   10.529%   $196.2332   $196.23   $196.25   $196.20  
  Purchase #7 $99.44   8.339%   $107.7323   $107.73   $107.75   $107.70  
  7 purchase totals = $877.78       $946.4619   $946.45   $946.50   $946.30