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 $108.41   13.701%   $123.2633   $123.26   $123.25   $123.30  
  Purchase #2 $213.93   11.379%   $238.2731   $238.27   $238.25   $238.30  
  Purchase #3 $139.66   12.147%   $156.6245   $156.62   $156.60   $156.60  
  Purchase #4 $198.98   11.257%   $221.3792   $221.38   $221.40   $221.40  
  Purchase #5 $88.65   6.710%   $94.5984   $94.60   $94.60   $94.60  
  Purchase #6 $95.68   12.258%   $107.4085   $107.41   $107.40   $107.40  
  Purchase #7 $237.83   7.621%   $255.955   $255.96   $255.95   $256.00  
  7 purchase totals = $1,083.14       $1,197.5020   $1,197.50   $1,197.45   $1,197.60