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	$27.54	10.135%	$30.3312	$30.33	$30.35	$30.30
Purchase #2	$197.32	5.290%	$207.7582	$207.76	$207.75	$207.80
Purchase #3	$168.82	9.814%	$185.388	$185.39	$185.40	$185.40
Purchase #4	$246.61	12.759%	$278.075	$278.08	$278.10	$278.10
Purchase #5	$53.26	11.519%	$59.395	$59.40	$59.40	$59.40
Purchase #6	$208.99	10.640%	$231.2265	$231.23	$231.25	$231.20
Purchase #7	$78.90	13.277%	$89.3756	$89.38	$89.40	$89.40
7 purchase totals =	$981.44		$1,081.5495	$1,081.57	$1,081.65	$1,081.60