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 $56.51   11.629%   $63.0815   $63.08   $63.10   $63.10  
  Purchase #2 $121.99   8.506%   $132.3665   $132.37   $132.35   $132.40  
  Purchase #3 $107.82   3.792%   $111.9085   $111.91   $111.90   $111.90  
  Purchase #4 $127.67   11.244%   $142.0252   $142.03   $142.05   $142.00  
  Purchase #5 $30.67   4.434%   $32.0299   $32.03   $32.05   $32.00  
  Purchase #6 $218.51   6.319%   $232.3176   $232.32   $232.30   $232.30  
  Purchase #7 $123.25   5.283%   $129.7613   $129.76   $129.75   $129.80  
  7 purchase totals = $786.42       $843.4905   $843.50   $843.50   $843.50