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 $92.99   5.113%   $97.7446   $97.74   $97.75   $97.70  
  Purchase #2 $99.45   13.832%   $113.2059   $113.21   $113.20   $113.20  
  Purchase #3 $49.86   6.640%   $53.1707   $53.17   $53.15   $53.20  
  Purchase #4 $191.93   6.608%   $204.6127   $204.61   $204.60   $204.60  
  Purchase #5 $236.63   7.213%   $253.6981   $253.70   $253.70   $253.70  
  Purchase #6 $25.85   13.256%   $29.2767   $29.28   $29.30   $29.30  
  Purchase #7 $227.67   12.777%   $256.7594   $256.76   $256.75   $256.80  
  7 purchase totals = $924.38       $1,008.4681   $1,008.47   $1,008.45   $1,008.50