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 $62.77   7.217%   $67.3001   $67.30   $67.30   $67.30  
  Purchase #2 $94.31   4.594%   $98.6426   $98.64   $98.65   $98.60  
  Purchase #3 $240.94   4.872%   $252.6786   $252.68   $252.70   $252.70  
  Purchase #4 $167.36   7.291%   $179.5622   $179.56   $179.55   $179.60  
  Purchase #5 $218.98   7.110%   $234.5495   $234.55   $234.55   $234.50  
  Purchase #6 $90.72   13.695%   $103.1441   $103.14   $103.15   $103.10  
  Purchase #7 $13.31   7.328%   $14.2854   $14.29   $14.30   $14.30  
  7 purchase totals = $888.39       $950.1625   $950.16   $950.20   $950.10