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 $245.93   13.526%   $279.1945   $279.19   $279.20   $279.20  
  Purchase #2 $140.83   3.380%   $145.5901   $145.59   $145.60   $145.60  
  Purchase #3 $174.77   9.762%   $191.831   $191.83   $191.85   $191.80  
  Purchase #4 $120.78   9.397%   $132.1297   $132.13   $132.15   $132.10  
  Purchase #5 $36.82   6.621%   $39.2579   $39.26   $39.25   $39.30  
  Purchase #6 $6.95   4.683%   $7.2755   $7.28   $7.30   $7.30  
  Purchase #7 $239.62   10.620%   $265.0676   $265.07   $265.05   $265.10  
  7 purchase totals = $965.70       $1,060.3463   $1,060.35   $1,060.40   $1,060.40