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 $204.48   10.467%   $225.8829   $225.88   $225.90   $225.90  
  Purchase #2 $37.54   9.155%   $40.9768   $40.98   $41.00   $41.00  
  Purchase #3 $61.81   4.742%   $64.741   $64.74   $64.75   $64.70  
  Purchase #4 $184.55   11.662%   $206.0722   $206.07   $206.05   $206.10  
  Purchase #5 $16.57   13.658%   $18.8331   $18.83   $18.85   $18.80  
  Purchase #6 $47.54   11.491%   $53.0028   $53.00   $53.00   $53.00  
  Purchase #7 $140.93   12.668%   $158.783   $158.78   $158.80   $158.80  
  7 purchase totals = $693.42       $768.2918   $768.28   $768.35   $768.30