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	$33.85	5.539%	$35.725	$35.73	$35.75	$35.70
Purchase #2	$46.72	11.309%	$52.0036	$52.00	$52.00	$52.00
Purchase #3	$26.33	4.701%	$27.5678	$27.57	$27.55	$27.60
Purchase #4	$34.85	6.140%	$36.9898	$36.99	$37.00	$37.00
Purchase #5	$94.78	9.109%	$103.4135	$103.41	$103.40	$103.40
Purchase #6	$138.85	12.789%	$156.6075	$156.61	$156.60	$156.60
Purchase #7	$160.41	3.168%	$165.4918	$165.49	$165.50	$165.50
7 purchase totals =	$535.79		$577.7990	$577.80	$577.80	$577.80