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 $250.89   5.616%   $264.98   $264.98   $265.00   $265.00  
  Purchase #2 $104.61   12.677%   $117.8714   $117.87   $117.85   $117.90  
  Purchase #3 $244.56   5.362%   $257.6733   $257.67   $257.65   $257.70  
  Purchase #4 $46.72   4.135%   $48.6519   $48.65   $48.65   $48.70  
  Purchase #5 $104.93   8.451%   $113.7976   $113.80   $113.80   $113.80  
  Purchase #6 $32.67   13.353%   $37.0324   $37.03   $37.05   $37.00  
  Purchase #7 $178.82   3.570%   $185.2039   $185.20   $185.20   $185.20  
  7 purchase totals = $963.20       $1,025.2105   $1,025.20   $1,025.20   $1,025.30