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	$86.61	4.289%	$90.3247	$90.32	$90.30	$90.30
Purchase #2	$195.74	6.324%	$208.1186	$208.12	$208.10	$208.10
Purchase #3	$33.84	3.504%	$35.0258	$35.03	$35.05	$35.00
Purchase #4	$57.51	4.113%	$59.8754	$59.88	$59.90	$59.90
Purchase #5	$60.57	3.558%	$62.7251	$62.73	$62.75	$62.70
Purchase #6	$7.73	4.501%	$8.0779	$8.08	$8.10	$8.10
Purchase #7	$136.57	13.826%	$155.4522	$155.45	$155.45	$155.50
7 purchase totals =	$578.57		$619.5997	$619.61	$619.65	$619.60