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 $183.56   13.832%   $208.95   $208.95   $208.95   $209.00  
  Purchase #2 $76.45   10.836%   $84.7341   $84.73   $84.75   $84.70  
  Purchase #3 $37.84   8.834%   $41.1828   $41.18   $41.20   $41.20  
  Purchase #4 $246.76   6.706%   $263.3077   $263.31   $263.30   $263.30  
  Purchase #5 $209.66   6.836%   $223.9924   $223.99   $224.00   $224.00  
  Purchase #6 $201.99   5.828%   $213.762   $213.76   $213.75   $213.80  
  Purchase #7 $32.73   3.315%   $33.815   $33.82   $33.80   $33.80  
  7 purchase totals = $988.99       $1,069.7440   $1,069.74   $1,069.75   $1,069.80