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 $67.96   11.216%   $75.5824   $75.58   $75.60   $75.60  
  Purchase #2 $54.88   8.728%   $59.6699   $59.67   $59.65   $59.70  
  Purchase #3 $50.50   4.445%   $52.7447   $52.74   $52.75   $52.70  
  Purchase #4 $21.49   13.541%   $24.4   $24.40   $24.40   $24.40  
  Purchase #5 $63.70   11.749%   $71.1841   $71.18   $71.20   $71.20  
  Purchase #6 $200.82   11.794%   $224.5047   $224.50   $224.50   $224.50  
  Purchase #7 $193.75   6.251%   $205.8613   $205.86   $205.85   $205.90  
  7 purchase totals = $653.10       $713.9471   $713.93   $713.95   $714.00