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 $49.42   13.637%   $56.1594   $56.16   $56.15   $56.20  
  Purchase #2 $35.96   4.640%   $37.6285   $37.63   $37.65   $37.60  
  Purchase #3 $77.59   6.627%   $82.7319   $82.73   $82.75   $82.70  
  Purchase #4 $241.87   6.416%   $257.3884   $257.39   $257.40   $257.40  
  Purchase #5 $58.75   4.729%   $61.5283   $61.53   $61.55   $61.50  
  Purchase #6 $111.29   13.281%   $126.0704   $126.07   $126.05   $126.10  
  Purchase #7 $100.82   5.307%   $106.1705   $106.17   $106.15   $106.20  
  7 purchase totals = $675.70       $727.6774   $727.68   $727.70   $727.70