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 $62.32   10.243%   $68.7034   $68.70   $68.70   $68.70  
  Purchase #2 $44.94   9.584%   $49.247   $49.25   $49.25   $49.20  
  Purchase #3 $90.63   4.542%   $94.7464   $94.75   $94.75   $94.70  
  Purchase #4 $200.76   7.231%   $215.277   $215.28   $215.30   $215.30  
  Purchase #5 $173.59   6.327%   $184.573   $184.57   $184.55   $184.60  
  Purchase #6 $120.91   8.708%   $131.4388   $131.44   $131.45   $131.40  
  Purchase #7 $224.47   6.511%   $239.0852   $239.09   $239.10   $239.10  
  7 purchase totals = $917.62       $983.0708   $983.08   $983.10   $983.00