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 $103.91   13.678%   $118.1228   $118.12   $118.10   $118.10  
  Purchase #2 $208.36   5.415%   $219.6427   $219.64   $219.65   $219.60  
  Purchase #3 $203.39   13.568%   $230.986   $230.99   $231.00   $231.00  
  Purchase #4 $248.25   6.401%   $264.1405   $264.14   $264.15   $264.10  
  Purchase #5 $237.88   12.855%   $268.4595   $268.46   $268.45   $268.50  
  Purchase #6 $93.37   7.394%   $100.2738   $100.27   $100.25   $100.30  
  Purchase #7 $246.87   10.673%   $273.2184   $273.22   $273.20   $273.20  
  7 purchase totals = $1,342.03       $1,474.8437   $1,474.84   $1,474.80   $1,474.80