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 $242.48   6.377%   $257.9429   $257.94   $257.95   $257.90  
  Purchase #2 $30.93   6.302%   $32.8792   $32.88   $32.90   $32.90  
  Purchase #3 $65.81   3.213%   $67.9245   $67.92   $67.90   $67.90  
  Purchase #4 $56.53   6.593%   $60.257   $60.26   $60.25   $60.30  
  Purchase #5 $61.69   8.818%   $67.1298   $67.13   $67.15   $67.10  
  Purchase #6 $203.78   9.528%   $223.1962   $223.20   $223.20   $223.20  
  Purchase #7 $48.98   7.580%   $52.6927   $52.69   $52.70   $52.70  
  7 purchase totals = $710.20       $762.0223   $762.02   $762.05   $762.00