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 $244.55   13.213%   $276.8624   $276.86   $276.85   $276.90  
  Purchase #2 $222.64   5.399%   $234.6603   $234.66   $234.65   $234.70  
  Purchase #3 $29.60   10.300%   $32.6488   $32.65   $32.65   $32.60  
  Purchase #4 $22.25   11.632%   $24.8381   $24.84   $24.85   $24.80  
  Purchase #5 $205.91   7.475%   $221.3018   $221.30   $221.30   $221.30  
  Purchase #6 $224.59   12.501%   $252.666   $252.67   $252.65   $252.70  
  Purchase #7 $215.69   6.272%   $229.2181   $229.22   $229.20   $229.20  
  7 purchase totals = $1,165.23       $1,272.1955   $1,272.20   $1,272.15   $1,272.20