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 $228.86   5.518%   $241.4885   $241.49   $241.50   $241.50  
  Purchase #2 $23.88   4.797%   $25.0255   $25.03   $25.05   $25.00  
  Purchase #3 $39.57   9.777%   $43.4388   $43.44   $43.45   $43.40  
  Purchase #4 $178.74   5.343%   $188.2901   $188.29   $188.30   $188.30  
  Purchase #5 $58.87   8.274%   $63.7409   $63.74   $63.75   $63.70  
  Purchase #6 $192.31   12.655%   $216.6468   $216.65   $216.65   $216.60  
  Purchase #7 $174.59   4.601%   $182.6229   $182.62   $182.60   $182.60  
  7 purchase totals = $896.82       $961.2535   $961.26   $961.30   $961.10