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 $246.65   7.612%   $265.425   $265.43   $265.45   $265.40  
  Purchase #2 $139.35   4.213%   $145.2208   $145.22   $145.20   $145.20  
  Purchase #3 $142.77   9.554%   $156.4102   $156.41   $156.40   $156.40  
  Purchase #4 $117.93   4.731%   $123.5093   $123.51   $123.50   $123.50  
  Purchase #5 $214.85   4.582%   $224.6944   $224.69   $224.70   $224.70  
  Purchase #6 $244.91   5.142%   $257.5033   $257.50   $257.50   $257.50  
  Purchase #7 $59.62   6.640%   $63.5788   $63.58   $63.60   $63.60  
  7 purchase totals = $1,166.08       $1,236.3418   $1,236.34   $1,236.35   $1,236.30