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 $222.31   13.788%   $252.9621   $252.96   $252.95   $253.00  
  Purchase #2 $186.57   11.615%   $208.2401   $208.24   $208.25   $208.20  
  Purchase #3 $243.70   11.808%   $272.4761   $272.48   $272.50   $272.50  
  Purchase #4 $211.70   5.219%   $222.7486   $222.75   $222.75   $222.70  
  Purchase #5 $247.81   8.485%   $268.8367   $268.84   $268.85   $268.80  
  Purchase #6 $177.27   4.480%   $185.2117   $185.21   $185.20   $185.20  
  Purchase #7 $125.54   9.368%   $137.3006   $137.30   $137.30   $137.30  
  7 purchase totals = $1,414.90       $1,547.7759   $1,547.78   $1,547.80   $1,547.70