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 $190.88   9.863%   $209.7065   $209.71   $209.70   $209.70  
  Purchase #2 $61.71   4.344%   $64.3907   $64.39   $64.40   $64.40  
  Purchase #3 $31.28   4.519%   $32.6935   $32.69   $32.70   $32.70  
  Purchase #4 $194.57   4.638%   $203.5942   $203.59   $203.60   $203.60  
  Purchase #5 $193.92   5.561%   $204.7039   $204.70   $204.70   $204.70  
  Purchase #6 $213.62   6.150%   $226.7576   $226.76   $226.75   $226.80  
  Purchase #7 $50.47   4.684%   $52.834   $52.83   $52.85   $52.80  
  7 purchase totals = $936.45       $994.6804   $994.67   $994.70   $994.70