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 $233.37   13.662%   $265.253   $265.25   $265.25   $265.30  
  Purchase #2 $194.27   10.564%   $214.7927   $214.79   $214.80   $214.80  
  Purchase #3 $208.99   10.335%   $230.5891   $230.59   $230.60   $230.60  
  Purchase #4 $158.41   11.292%   $176.2977   $176.30   $176.30   $176.30  
  Purchase #5 $146.52   8.850%   $159.487   $159.49   $159.50   $159.50  
  Purchase #6 $215.72   13.428%   $244.6869   $244.69   $244.70   $244.70  
  Purchase #7 $37.74   3.704%   $39.1379   $39.14   $39.15   $39.10  
  7 purchase totals = $1,195.02       $1,330.2443   $1,330.25   $1,330.30   $1,330.30