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	$87.36	3.742%	$90.629	$90.63	$90.65	$90.60
Purchase #2	$105.96	3.165%	$109.3136	$109.31	$109.30	$109.30
Purchase #3	$196.85	7.430%	$211.476	$211.48	$211.50	$211.50
Purchase #4	$134.33	6.589%	$143.181	$143.18	$143.20	$143.20
Purchase #5	$49.69	12.839%	$56.0697	$56.07	$56.05	$56.10
Purchase #6	$55.26	10.548%	$61.0888	$61.09	$61.10	$61.10
Purchase #7	$159.29	12.199%	$178.7218	$178.72	$178.70	$178.70
7 purchase totals =	$788.74		$850.4799	$850.48	$850.50	$850.50