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	$9.74	4.834%	$10.2108	$10.21	$10.20	$10.20
Purchase #2	$62.41	13.765%	$71.0007	$71.00	$71.00	$71.00
Purchase #3	$132.89	5.308%	$139.9438	$139.94	$139.95	$139.90
Purchase #4	$166.98	11.335%	$185.9072	$185.91	$185.90	$185.90
Purchase #5	$118.89	13.803%	$135.3004	$135.30	$135.30	$135.30
Purchase #6	$13.87	9.773%	$15.2255	$15.23	$15.25	$15.20
Purchase #7	$122.73	13.628%	$139.4556	$139.46	$139.45	$139.50
7 purchase totals =	$627.51		$697.0440	$697.05	$697.05	$697.00