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	$232.96	7.445%	$250.3039	$250.30	$250.30	$250.30
Purchase #2	$26.54	12.737%	$29.9204	$29.92	$29.90	$29.90
Purchase #3	$129.76	13.324%	$147.0492	$147.05	$147.05	$147.00
Purchase #4	$123.44	13.686%	$140.334	$140.33	$140.35	$140.30
Purchase #5	$234.76	8.724%	$255.2405	$255.24	$255.25	$255.20
Purchase #6	$179.48	6.663%	$191.4388	$191.44	$191.45	$191.40
Purchase #7	$80.59	3.519%	$83.426	$83.43	$83.45	$83.40
7 purchase totals =	$1,007.53		$1,097.7128	$1,097.71	$1,097.75	$1,097.50