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 $183.26   4.670%   $191.8182   $191.82   $191.80   $191.80  
  Purchase #2 $178.63   7.229%   $191.5432   $191.54   $191.55   $191.50  
  Purchase #3 $96.25   11.720%   $107.5305   $107.53   $107.55   $107.50  
  Purchase #4 $44.76   6.260%   $47.562   $47.56   $47.55   $47.60  
  Purchase #5 $191.47   13.647%   $217.5999   $217.60   $217.60   $217.60  
  Purchase #6 $174.35   11.265%   $193.9905   $193.99   $194.00   $194.00  
  Purchase #7 $168.39   13.511%   $191.1412   $191.14   $191.15   $191.10  
  7 purchase totals = $1,037.11       $1,141.1855   $1,141.18   $1,141.20   $1,141.10