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	$85.38	5.611%	$90.1707	$90.17	$90.15	$90.20
Purchase #2	$86.27	8.718%	$93.791	$93.79	$93.80	$93.80
Purchase #3	$110.89	5.406%	$116.8847	$116.88	$116.90	$116.90
Purchase #4	$54.56	12.115%	$61.1699	$61.17	$61.15	$61.20
Purchase #5	$248.45	8.168%	$268.7434	$268.74	$268.75	$268.70
Purchase #6	$171.42	11.501%	$191.135	$191.14	$191.15	$191.10
Purchase #7	$127.82	4.414%	$133.462	$133.46	$133.45	$133.50
7 purchase totals =	$884.79		$955.3567	$955.35	$955.35	$955.40