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	$36.50	11.553%	$40.7168	$40.72	$40.70	$40.70
Purchase #2	$54.87	4.650%	$57.4215	$57.42	$57.40	$57.40
Purchase #3	$36.67	4.742%	$38.4089	$38.41	$38.40	$38.40
Purchase #4	$167.80	4.514%	$175.3745	$175.37	$175.35	$175.40
Purchase #5	$236.31	7.844%	$254.8462	$254.85	$254.85	$254.80
Purchase #6	$40.33	12.555%	$45.3934	$45.39	$45.40	$45.40
Purchase #7	$87.86	7.461%	$94.4152	$94.42	$94.40	$94.40
7 purchase totals =	$660.34		$706.5765	$706.58	$706.50	$706.50