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	$41.41	7.538%	$44.5315	$44.53	$44.55	$44.50
Purchase #2	$227.76	3.150%	$234.9344	$234.93	$234.95	$234.90
Purchase #3	$75.92	3.650%	$78.6911	$78.69	$78.70	$78.70
Purchase #4	$43.78	4.808%	$45.8849	$45.88	$45.90	$45.90
Purchase #5	$75.83	3.345%	$78.3665	$78.37	$78.35	$78.40
Purchase #6	$11.77	9.477%	$12.8854	$12.89	$12.90	$12.90
Purchase #7	$161.48	6.421%	$171.8486	$171.85	$171.85	$171.80
7 purchase totals =	$637.95		$667.1424	$667.14	$667.20	$667.10