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 $116.63   12.372%   $131.0595   $131.06   $131.05   $131.10  
  Purchase #2 $112.42   7.358%   $120.6919   $120.69   $120.70   $120.70  
  Purchase #3 $182.45   3.541%   $188.9106   $188.91   $188.90   $188.90  
  Purchase #4 $243.94   13.350%   $276.506   $276.51   $276.50   $276.50  
  Purchase #5 $80.66   4.178%   $84.03   $84.03   $84.05   $84.00  
  Purchase #6 $89.56   5.431%   $94.424   $94.42   $94.40   $94.40  
  Purchase #7 $132.76   12.711%   $149.6351   $149.64   $149.65   $149.60  
  7 purchase totals = $958.42       $1,045.2571   $1,045.26   $1,045.25   $1,045.20