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 $229.56   8.784%   $249.7246   $249.72   $249.70   $249.70  
  Purchase #2 $58.26   11.458%   $64.9354   $64.94   $64.95   $64.90  
  Purchase #3 $160.95   8.785%   $175.0895   $175.09   $175.10   $175.10  
  Purchase #4 $181.82   5.564%   $191.9365   $191.94   $191.95   $191.90  
  Purchase #5 $181.99   3.678%   $188.6836   $188.68   $188.70   $188.70  
  Purchase #6 $206.87   5.104%   $217.4286   $217.43   $217.45   $217.40  
  Purchase #7 $21.62   3.292%   $22.3317   $22.33   $22.35   $22.30  
  7 purchase totals = $1,041.07       $1,110.1299   $1,110.13   $1,110.20   $1,110.00