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 $108.93   9.492%   $119.2696   $119.27   $119.25   $119.30  
  Purchase #2 $191.59   13.572%   $217.5926   $217.59   $217.60   $217.60  
  Purchase #3 $201.42   6.187%   $213.8819   $213.88   $213.90   $213.90  
  Purchase #4 $215.76   13.229%   $244.3029   $244.30   $244.30   $244.30  
  Purchase #5 $101.91   11.568%   $113.6989   $113.70   $113.70   $113.70  
  Purchase #6 $140.96   12.213%   $158.1754   $158.18   $158.20   $158.20  
  Purchase #7 $178.27   3.658%   $184.7911   $184.79   $184.80   $184.80  
  7 purchase totals = $1,138.84       $1,251.7124   $1,251.71   $1,251.75   $1,251.80