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 $239.45   3.254%   $247.2417   $247.24   $247.25   $247.20  
  Purchase #2 $59.72   3.795%   $61.9864   $61.99   $62.00   $62.00  
  Purchase #3 $145.83   9.749%   $160.047   $160.05   $160.05   $160.00  
  Purchase #4 $148.75   3.425%   $153.8447   $153.84   $153.85   $153.80  
  Purchase #5 $102.66   11.560%   $114.5275   $114.53   $114.55   $114.50  
  Purchase #6 $160.48   4.705%   $168.0306   $168.03   $168.05   $168.00  
  Purchase #7 $29.90   5.312%   $31.4883   $31.49   $31.50   $31.50  
  7 purchase totals = $886.79       $937.1662   $937.17   $937.25   $937.00