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 $211.52   11.687%   $236.2403   $236.24   $236.25   $236.20  
  Purchase #2 $226.91   3.825%   $235.5893   $235.59   $235.60   $235.60  
  Purchase #3 $223.62   11.454%   $249.2334   $249.23   $249.25   $249.20  
  Purchase #4 $49.76   8.242%   $53.8612   $53.86   $53.85   $53.90  
  Purchase #5 $177.43   3.114%   $182.9552   $182.96   $182.95   $183.00  
  Purchase #6 $222.47   5.618%   $234.9684   $234.97   $234.95   $235.00  
  Purchase #7 $100.91   9.580%   $110.5772   $110.58   $110.60   $110.60  
  7 purchase totals = $1,212.62       $1,303.4250   $1,303.43   $1,303.45   $1,303.50