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 $244.51   8.691%   $265.7604   $265.76   $265.75   $265.80  
  Purchase #2 $228.41   4.469%   $238.6176   $238.62   $238.60   $238.60  
  Purchase #3 $154.87   3.410%   $160.1511   $160.15   $160.15   $160.20  
  Purchase #4 $48.84   13.663%   $55.513   $55.51   $55.50   $55.50  
  Purchase #5 $125.66   9.617%   $137.7447   $137.74   $137.75   $137.70  
  Purchase #6 $183.39   13.731%   $208.5713   $208.57   $208.55   $208.60  
  Purchase #7 $162.51   5.764%   $171.8771   $171.88   $171.90   $171.90  
  7 purchase totals = $1,148.19       $1,238.2352   $1,238.23   $1,238.20   $1,238.30