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 $95.43   8.124%   $103.1827   $103.18   $103.20   $103.20  
  Purchase #2 $8.52   11.441%   $9.4948   $9.49   $9.50   $9.50  
  Purchase #3 $114.94   4.109%   $119.6629   $119.66   $119.65   $119.70  
  Purchase #4 $236.36   3.617%   $244.9091   $244.91   $244.90   $244.90  
  Purchase #5 $139.76   3.244%   $144.2938   $144.29   $144.30   $144.30  
  Purchase #6 $211.44   6.834%   $225.8898   $225.89   $225.90   $225.90  
  Purchase #7 $97.71   7.811%   $105.3421   $105.34   $105.35   $105.30  
  7 purchase totals = $904.16       $952.7752   $952.76   $952.80   $952.80