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	$88.91	13.861%	$101.2338	$101.23	$101.25	$101.20
Purchase #2	$233.95	6.218%	$248.497	$248.50	$248.50	$248.50
Purchase #3	$88.83	12.173%	$99.6433	$99.64	$99.65	$99.60
Purchase #4	$225.27	8.766%	$245.0172	$245.02	$245.00	$245.00
Purchase #5	$234.91	7.323%	$252.1125	$252.11	$252.10	$252.10
Purchase #6	$127.86	13.180%	$144.7119	$144.71	$144.70	$144.70
Purchase #7	$91.87	9.601%	$100.6904	$100.69	$100.70	$100.70
7 purchase totals =	$1,091.60		$1,191.9061	$1,191.90	$1,191.90	$1,191.80