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	$237.70	5.303%	$250.3052	$250.31	$250.30	$250.30
Purchase #2	$80.39	10.804%	$89.0753	$89.08	$89.10	$89.10
Purchase #3	$182.89	4.839%	$191.74	$191.74	$191.75	$191.70
Purchase #4	$208.57	6.529%	$222.1875	$222.19	$222.20	$222.20
Purchase #5	$141.98	6.185%	$150.7615	$150.76	$150.75	$150.80
Purchase #6	$214.26	6.587%	$228.3733	$228.37	$228.35	$228.40
Purchase #7	$133.83	13.370%	$151.7231	$151.72	$151.70	$151.70
7 purchase totals =	$1,199.62		$1,284.1659	$1,284.17	$1,284.15	$1,284.20