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 $246.75   11.576%   $275.3138   $275.31   $275.30   $275.30  
  Purchase #2 $14.50   4.145%   $15.101   $15.10   $15.10   $15.10  
  Purchase #3 $110.35   12.749%   $124.4185   $124.42   $124.40   $124.40  
  Purchase #4 $191.88   11.353%   $213.6641   $213.66   $213.65   $213.70  
  Purchase #5 $175.74   6.314%   $186.8362   $186.84   $186.85   $186.80  
  Purchase #6 $47.40   9.550%   $51.9267   $51.93   $51.95   $51.90  
  Purchase #7 $190.65   9.391%   $208.5539   $208.55   $208.55   $208.60  
  7 purchase totals = $977.27       $1,075.8142   $1,075.81   $1,075.80   $1,075.80