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 $54.41   8.260%   $58.9043   $58.90   $58.90   $58.90  
  Purchase #2 $209.66   6.267%   $222.7994   $222.80   $222.80   $222.80  
  Purchase #3 $145.53   13.543%   $165.2391   $165.24   $165.25   $165.20  
  Purchase #4 $105.73   8.758%   $114.9898   $114.99   $115.00   $115.00  
  Purchase #5 $178.76   11.680%   $199.6392   $199.64   $199.65   $199.60  
  Purchase #6 $59.51   11.414%   $66.3025   $66.30   $66.30   $66.30  
  Purchase #7 $195.51   7.222%   $209.6297   $209.63   $209.65   $209.60  
  7 purchase totals = $949.11       $1,037.5040   $1,037.50   $1,037.55   $1,037.40