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 $189.49   3.169%   $195.4949   $195.49   $195.50   $195.50  
  Purchase #2 $88.71   9.638%   $97.2599   $97.26   $97.25   $97.30  
  Purchase #3 $193.75   6.422%   $206.1926   $206.19   $206.20   $206.20  
  Purchase #4 $146.41   6.388%   $155.7627   $155.76   $155.75   $155.80  
  Purchase #5 $108.61   12.697%   $122.4002   $122.40   $122.40   $122.40  
  Purchase #6 $238.36   4.539%   $249.1792   $249.18   $249.20   $249.20  
  Purchase #7 $156.44   5.560%   $165.1381   $165.14   $165.15   $165.10  
  7 purchase totals = $1,121.77       $1,191.4276   $1,191.42   $1,191.45   $1,191.50