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	$33.59	11.596%	$37.4851	$37.49	$37.50	$37.50
Purchase #2	$141.35	6.529%	$150.5787	$150.58	$150.60	$150.60
Purchase #3	$118.77	5.590%	$125.4092	$125.41	$125.40	$125.40
Purchase #4	$105.73	5.454%	$111.4965	$111.50	$111.50	$111.50
Purchase #5	$248.31	11.268%	$276.2896	$276.29	$276.30	$276.30
Purchase #6	$84.91	4.621%	$88.8337	$88.83	$88.85	$88.80
Purchase #7	$30.95	6.432%	$32.9407	$32.94	$32.95	$32.90
7 purchase totals =	$763.61		$823.0335	$823.04	$823.10	$823.00