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 $249.99   7.485%   $268.7018   $268.70   $268.70   $268.70  
  Purchase #2 $214.44   11.634%   $239.3879   $239.39   $239.40   $239.40  
  Purchase #3 $111.71   12.494%   $125.667   $125.67   $125.65   $125.70  
  Purchase #4 $156.91   6.201%   $166.64   $166.64   $166.65   $166.60  
  Purchase #5 $143.60   9.626%   $157.4229   $157.42   $157.40   $157.40  
  Purchase #6 $38.69   3.590%   $40.079   $40.08   $40.10   $40.10  
  Purchase #7 $108.67   10.689%   $120.2857   $120.29   $120.30   $120.30  
  7 purchase totals = $1,024.01       $1,118.1843   $1,118.19   $1,118.20   $1,118.20