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 $219.40   3.242%   $226.5129   $226.51   $226.50   $226.50  
  Purchase #2 $44.62   11.597%   $49.7946   $49.79   $49.80   $49.80  
  Purchase #3 $79.74   5.622%   $84.223   $84.22   $84.20   $84.20  
  Purchase #4 $148.93   3.697%   $154.4359   $154.44   $154.45   $154.40  
  Purchase #5 $171.80   9.310%   $187.7946   $187.79   $187.80   $187.80  
  Purchase #6 $169.99   12.688%   $191.5583   $191.56   $191.55   $191.60  
  Purchase #7 $119.30   7.117%   $127.7906   $127.79   $127.80   $127.80  
  7 purchase totals = $953.78       $1,022.1099   $1,022.10   $1,022.10   $1,022.10