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 $66.66   11.482%   $74.3139   $74.31   $74.30   $74.30  
  Purchase #2 $53.85   3.501%   $55.7353   $55.74   $55.75   $55.70  
  Purchase #3 $244.68   11.671%   $273.2366   $273.24   $273.25   $273.20  
  Purchase #4 $44.82   6.102%   $47.5549   $47.55   $47.55   $47.60  
  Purchase #5 $32.41   5.419%   $34.1663   $34.17   $34.15   $34.20  
  Purchase #6 $45.90   4.160%   $47.8094   $47.81   $47.80   $47.80  
  Purchase #7 $104.65   13.204%   $118.468   $118.47   $118.45   $118.50  
  7 purchase totals = $592.97       $651.2844   $651.29   $651.25   $651.30