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 $233.33   4.758%   $244.4318   $244.43   $244.45   $244.40  
  Purchase #2 $218.74   6.191%   $232.2822   $232.28   $232.30   $232.30  
  Purchase #3 $118.25   9.168%   $129.0912   $129.09   $129.10   $129.10  
  Purchase #4 $54.76   7.492%   $58.8626   $58.86   $58.85   $58.90  
  Purchase #5 $59.37   11.841%   $66.4   $66.40   $66.40   $66.40  
  Purchase #6 $183.44   8.445%   $198.9315   $198.93   $198.95   $198.90  
  Purchase #7 $101.32   12.373%   $113.8563   $113.86   $113.85   $113.90  
  7 purchase totals = $969.21       $1,043.8556   $1,043.85   $1,043.90   $1,043.90