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 $84.29   8.700%   $91.6232   $91.62   $91.60   $91.60  
  Purchase #2 $211.89   13.660%   $240.8342   $240.83   $240.85   $240.80  
  Purchase #3 $88.29   4.770%   $92.5014   $92.50   $92.50   $92.50  
  Purchase #4 $51.98   3.426%   $53.7608   $53.76   $53.75   $53.80  
  Purchase #5 $171.32   12.421%   $192.5997   $192.60   $192.60   $192.60  
  Purchase #6 $197.90   4.422%   $206.6511   $206.65   $206.65   $206.70  
  Purchase #7 $221.26   12.224%   $248.3068   $248.31   $248.30   $248.30  
  7 purchase totals = $1,026.93       $1,126.2772   $1,126.27   $1,126.25   $1,126.30