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 $206.61   3.414%   $213.6637   $213.66   $213.65   $213.70  
  Purchase #2 $85.97   13.821%   $97.8519   $97.85   $97.85   $97.90  
  Purchase #3 $239.84   10.167%   $264.2245   $264.22   $264.20   $264.20  
  Purchase #4 $153.35   11.302%   $170.6816   $170.68   $170.70   $170.70  
  Purchase #5 $147.90   5.272%   $155.6973   $155.70   $155.70   $155.70  
  Purchase #6 $136.27   12.267%   $152.9862   $152.99   $153.00   $153.00  
  Purchase #7 $158.70   8.105%   $171.5626   $171.56   $171.55   $171.60  
  7 purchase totals = $1,128.64       $1,226.6678   $1,226.66   $1,226.65   $1,226.80