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 $44.67   11.239%   $49.6905   $49.69   $49.70   $49.70  
  Purchase #2 $227.42   8.657%   $247.1077   $247.11   $247.10   $247.10  
  Purchase #3 $180.94   13.225%   $204.8693   $204.87   $204.85   $204.90  
  Purchase #4 $175.44   4.300%   $182.9839   $182.98   $183.00   $183.00  
  Purchase #5 $165.42   12.302%   $185.77   $185.77   $185.75   $185.80  
  Purchase #6 $67.94   11.466%   $75.73   $75.73   $75.75   $75.70  
  Purchase #7 $194.36   7.566%   $209.0653   $209.07   $209.05   $209.10  
  7 purchase totals = $1,056.19       $1,155.2167   $1,155.22   $1,155.20   $1,155.30