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	$12.89	7.313%	$13.8326	$13.83	$13.85	$13.80
Purchase #2	$110.52	8.333%	$119.7296	$119.73	$119.75	$119.70
Purchase #3	$39.56	4.403%	$41.3018	$41.30	$41.30	$41.30
Purchase #4	$193.52	8.290%	$209.5628	$209.56	$209.55	$209.60
Purchase #5	$78.77	10.598%	$87.118	$87.12	$87.10	$87.10
Purchase #6	$165.83	11.633%	$185.121	$185.12	$185.10	$185.10
Purchase #7	$232.42	7.825%	$250.6069	$250.61	$250.60	$250.60
7 purchase totals =	$833.51		$907.2727	$907.27	$907.25	$907.20