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 $61.98   10.682%   $68.6007   $68.60   $68.60   $68.60  
  Purchase #2 $128.31   9.392%   $140.3609   $140.36   $140.35   $140.40  
  Purchase #3 $43.38   7.661%   $46.7033   $46.70   $46.70   $46.70  
  Purchase #4 $170.65   4.678%   $178.633   $178.63   $178.65   $178.60  
  Purchase #5 $19.44   3.232%   $20.0683   $20.07   $20.05   $20.10  
  Purchase #6 $125.40   8.640%   $136.2346   $136.23   $136.25   $136.20  
  Purchase #7 $163.25   5.622%   $172.4279   $172.43   $172.45   $172.40  
  7 purchase totals = $712.41       $763.0287   $763.02   $763.05   $763.00