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 $175.61   10.679%   $194.3634   $194.36   $194.35   $194.40  
  Purchase #2 $145.37   7.694%   $156.5548   $156.55   $156.55   $156.60  
  Purchase #3 $114.90   7.397%   $123.3992   $123.40   $123.40   $123.40  
  Purchase #4 $192.30   9.443%   $210.4589   $210.46   $210.45   $210.50  
  Purchase #5 $47.67   13.260%   $53.991   $53.99   $54.00   $54.00  
  Purchase #6 $133.33   11.160%   $148.2096   $148.21   $148.20   $148.20  
  Purchase #7 $63.93   5.246%   $67.2838   $67.28   $67.30   $67.30  
  7 purchase totals = $873.11       $954.2607   $954.25   $954.25   $954.40