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 $208.26   9.126%   $227.2658   $227.27   $227.25   $227.30  
  Purchase #2 $118.39   11.714%   $132.2582   $132.26   $132.25   $132.30  
  Purchase #3 $45.59   3.744%   $47.2969   $47.30   $47.30   $47.30  
  Purchase #4 $32.99   4.464%   $34.4627   $34.46   $34.45   $34.50  
  Purchase #5 $84.39   3.398%   $87.2576   $87.26   $87.25   $87.30  
  Purchase #6 $115.50   7.199%   $123.8148   $123.81   $123.80   $123.80  
  Purchase #7 $211.26   4.445%   $220.6505   $220.65   $220.65   $220.70  
  7 purchase totals = $816.38       $873.0065   $873.01   $872.95   $873.20