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	$243.52	11.569%	$271.6928	$271.69	$271.70	$271.70
Purchase #2	$43.62	4.179%	$45.4429	$45.44	$45.45	$45.40
Purchase #3	$144.92	5.490%	$152.8761	$152.88	$152.90	$152.90
Purchase #4	$128.89	9.695%	$141.3859	$141.39	$141.40	$141.40
Purchase #5	$31.49	13.769%	$35.8259	$35.83	$35.85	$35.80
Purchase #6	$41.30	9.339%	$45.157	$45.16	$45.15	$45.20
Purchase #7	$113.52	10.483%	$125.4203	$125.42	$125.40	$125.40
7 purchase totals =	$747.26		$817.8009	$817.81	$817.85	$817.80