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 $248.60   13.361%   $281.8154   $281.82   $281.80   $281.80  
  Purchase #2 $73.27   3.315%   $75.6989   $75.70   $75.70   $75.70  
  Purchase #3 $161.77   10.305%   $178.4404   $178.44   $178.45   $178.40  
  Purchase #4 $236.68   9.314%   $258.7244   $258.72   $258.70   $258.70  
  Purchase #5 $209.82   12.582%   $236.2196   $236.22   $236.20   $236.20  
  Purchase #6 $64.32   9.443%   $70.3937   $70.39   $70.40   $70.40  
  Purchase #7 $226.39   8.107%   $244.7434   $244.74   $244.75   $244.70  
  7 purchase totals = $1,220.85       $1,346.0358   $1,346.03   $1,346.00   $1,345.90