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 $118.34   13.714%   $134.5691   $134.57   $134.55   $134.60  
  Purchase #2 $167.94   4.522%   $175.5342   $175.53   $175.55   $175.50  
  Purchase #3 $241.26   11.273%   $268.4572   $268.46   $268.45   $268.50  
  Purchase #4 $185.46   6.600%   $197.7004   $197.70   $197.70   $197.70  
  Purchase #5 $139.75   3.142%   $144.1409   $144.14   $144.15   $144.10  
  Purchase #6 $56.97   10.454%   $62.9256   $62.93   $62.95   $62.90  
  Purchase #7 $19.65   13.380%   $22.2792   $22.28   $22.30   $22.30  
  7 purchase totals = $929.37       $1,005.6066   $1,005.61   $1,005.65   $1,005.60