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 $108.94   9.500%   $119.2893   $119.29   $119.30   $119.30  
  Purchase #2 $126.27   11.476%   $140.7607   $140.76   $140.75   $140.80  
  Purchase #3 $152.54   13.724%   $173.4746   $173.47   $173.45   $173.50  
  Purchase #4 $185.31   11.159%   $205.9887   $205.99   $206.00   $206.00  
  Purchase #5 $221.87   8.589%   $240.9264   $240.93   $240.95   $240.90  
  Purchase #6 $25.26   8.830%   $27.4905   $27.49   $27.50   $27.50  
  Purchase #7 $165.25   12.107%   $185.2568   $185.26   $185.25   $185.30  
  7 purchase totals = $985.44       $1,093.1870   $1,093.19   $1,093.20   $1,093.30