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 $125.33   5.617%   $132.3698   $132.37   $132.35   $132.40  
  Purchase #2 $201.42   7.274%   $216.0713   $216.07   $216.05   $216.10  
  Purchase #3 $23.67   13.244%   $26.8049   $26.80   $26.80   $26.80  
  Purchase #4 $171.76   13.131%   $194.3138   $194.31   $194.30   $194.30  
  Purchase #5 $228.93   6.816%   $244.5339   $244.53   $244.55   $244.50  
  Purchase #6 $222.41   11.244%   $247.4178   $247.42   $247.40   $247.40  
  Purchase #7 $101.25   11.556%   $112.9505   $112.95   $112.95   $113.00  
  7 purchase totals = $1,074.77       $1,174.4620   $1,174.45   $1,174.40   $1,174.50