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 $55.77   8.154%   $60.3175   $60.32   $60.30   $60.30  
  Purchase #2 $66.71   7.695%   $71.8433   $71.84   $71.85   $71.80  
  Purchase #3 $119.28   5.615%   $125.9776   $125.98   $126.00   $126.00  
  Purchase #4 $29.87   8.205%   $32.3208   $32.32   $32.30   $32.30  
  Purchase #5 $123.26   5.138%   $129.5931   $129.59   $129.60   $129.60  
  Purchase #6 $203.71   13.806%   $231.8342   $231.83   $231.85   $231.80  
  Purchase #7 $53.89   9.184%   $58.8393   $58.84   $58.85   $58.80  
  7 purchase totals = $652.49       $710.7258   $710.72   $710.75   $710.60