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	$74.34	5.482%	$78.4153	$78.42	$78.40	$78.40
Purchase #2	$40.39	13.245%	$45.7397	$45.74	$45.75	$45.70
Purchase #3	$126.38	12.286%	$141.907	$141.91	$141.90	$141.90
Purchase #4	$236.64	13.781%	$269.2514	$269.25	$269.25	$269.30
Purchase #5	$177.33	9.851%	$194.7988	$194.80	$194.80	$194.80
Purchase #6	$131.56	9.355%	$143.8674	$143.87	$143.85	$143.90
Purchase #7	$185.44	11.753%	$207.2348	$207.23	$207.25	$207.20
7 purchase totals =	$972.08		$1,081.2144	$1,081.22	$1,081.20	$1,081.20