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 $84.86   12.757%   $95.6856   $95.69   $95.70   $95.70  
  Purchase #2 $144.41   11.263%   $160.6749   $160.67   $160.65   $160.70  
  Purchase #3 $108.37   9.407%   $118.5644   $118.56   $118.55   $118.60  
  Purchase #4 $120.48   11.462%   $134.2894   $134.29   $134.30   $134.30  
  Purchase #5 $228.71   13.804%   $260.2811   $260.28   $260.30   $260.30  
  Purchase #6 $245.93   12.866%   $277.5714   $277.57   $277.55   $277.60  
  Purchase #7 $174.66   12.474%   $196.4471   $196.45   $196.45   $196.40  
  7 purchase totals = $1,107.42       $1,243.5139   $1,243.51   $1,243.50   $1,243.60