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 $145.50   7.818%   $156.8752   $156.88   $156.90   $156.90  
  Purchase #2 $19.37   8.214%   $20.9611   $20.96   $20.95   $21.00  
  Purchase #3 $62.82   10.494%   $69.4123   $69.41   $69.40   $69.40  
  Purchase #4 $158.64   10.796%   $175.7668   $175.77   $175.75   $175.80  
  Purchase #5 $105.65   8.621%   $114.7581   $114.76   $114.75   $114.80  
  Purchase #6 $38.54   10.752%   $42.6838   $42.68   $42.70   $42.70  
  Purchase #7 $40.48   12.375%   $45.4894   $45.49   $45.50   $45.50  
  7 purchase totals = $571.00       $625.9467   $625.95   $625.95   $626.10