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 $48.77   9.162%   $53.2383   $53.24   $53.25   $53.20  
  Purchase #2 $133.76   4.610%   $139.9263   $139.93   $139.95   $139.90  
  Purchase #3 $248.25   4.277%   $258.8677   $258.87   $258.85   $258.90  
  Purchase #4 $211.55   7.259%   $226.9064   $226.91   $226.90   $226.90  
  Purchase #5 $250.92   6.550%   $267.3553   $267.36   $267.35   $267.40  
  Purchase #6 $56.48   13.832%   $64.2923   $64.29   $64.30   $64.30  
  Purchase #7 $41.33   3.829%   $42.9125   $42.91   $42.90   $42.90  
  7 purchase totals = $991.06       $1,053.4988   $1,053.51   $1,053.50   $1,053.50