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	$50.69	9.132%	$55.319	$55.32	$55.30	$55.30
Purchase #2	$167.70	7.632%	$180.4989	$180.50	$180.50	$180.50
Purchase #3	$140.42	8.608%	$152.5074	$152.51	$152.50	$152.50
Purchase #4	$242.62	12.760%	$273.5783	$273.58	$273.60	$273.60
Purchase #5	$18.41	4.173%	$19.1782	$19.18	$19.20	$19.20
Purchase #6	$79.40	11.153%	$88.2555	$88.26	$88.25	$88.30
Purchase #7	$56.71	8.721%	$61.6557	$61.66	$61.65	$61.70
7 purchase totals =	$755.95		$830.9930	$831.01	$831.00	$831.10