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 $156.27   7.308%   $167.6902   $167.69   $167.70   $167.70  
  Purchase #2 $14.38   8.808%   $15.6466   $15.65   $15.65   $15.60  
  Purchase #3 $49.50   11.702%   $55.2925   $55.29   $55.30   $55.30  
  Purchase #4 $79.37   11.123%   $88.1983   $88.20   $88.20   $88.20  
  Purchase #5 $121.94   3.309%   $125.975   $125.98   $126.00   $126.00  
  Purchase #6 $69.98   4.551%   $73.1648   $73.16   $73.15   $73.20  
  Purchase #7 $246.32   4.328%   $256.9807   $256.98   $257.00   $257.00  
  7 purchase totals = $737.76       $782.9481   $782.95   $783.00   $783.00