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	$49.66	10.595%	$54.9215	$54.92	$54.90	$54.90
Purchase #2	$250.29	13.577%	$284.2719	$284.27	$284.25	$284.30
Purchase #3	$174.97	10.374%	$193.1214	$193.12	$193.10	$193.10
Purchase #4	$163.47	10.383%	$180.4431	$180.44	$180.45	$180.40
Purchase #5	$30.62	9.275%	$33.46	$33.46	$33.45	$33.50
Purchase #6	$156.77	5.277%	$165.0428	$165.04	$165.05	$165.00
Purchase #7	$100.96	8.111%	$109.1489	$109.15	$109.15	$109.10
7 purchase totals =	$926.74		$1,020.4096	$1,020.40	$1,020.35	$1,020.30