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	$35.76	12.780%	$40.3301	$40.33	$40.35	$40.30
Purchase #2	$49.93	7.358%	$53.6038	$53.60	$53.60	$53.60
Purchase #3	$52.59	13.279%	$59.5734	$59.57	$59.55	$59.60
Purchase #4	$156.82	5.476%	$165.4075	$165.41	$165.40	$165.40
Purchase #5	$43.88	3.746%	$45.5237	$45.52	$45.50	$45.50
Purchase #6	$57.52	11.713%	$64.2573	$64.26	$64.25	$64.30
Purchase #7	$140.73	13.447%	$159.654	$159.65	$159.65	$159.70
7 purchase totals =	$537.23		$588.3498	$588.34	$588.30	$588.40