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 $228.48   6.662%   $243.7013   $243.70   $243.70   $243.70  
  Purchase #2 $228.99   13.390%   $259.6518   $259.65   $259.65   $259.70  
  Purchase #3 $227.72   4.325%   $237.5689   $237.57   $237.55   $237.60  
  Purchase #4 $207.25   10.316%   $228.6299   $228.63   $228.65   $228.60  
  Purchase #5 $48.77   13.808%   $55.5042   $55.50   $55.50   $55.50  
  Purchase #6 $49.99   3.562%   $51.7706   $51.77   $51.75   $51.80  
  Purchase #7 $6.57   6.275%   $6.9823   $6.98   $7.00   $7.00  
  7 purchase totals = $997.77       $1,083.8090   $1,083.80   $1,083.80   $1,083.90