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	$191.76	3.845%	$199.1332	$199.13	$199.15	$199.10
Purchase #2	$240.82	9.858%	$264.56	$264.56	$264.55	$264.60
Purchase #3	$37.84	11.649%	$42.248	$42.25	$42.25	$42.20
Purchase #4	$130.76	4.513%	$136.6612	$136.66	$136.65	$136.70
Purchase #5	$67.86	13.655%	$77.1263	$77.13	$77.15	$77.10
Purchase #6	$102.28	13.739%	$116.3322	$116.33	$116.35	$116.30
Purchase #7	$83.81	3.600%	$86.8272	$86.83	$86.85	$86.80
7 purchase totals =	$855.13		$922.8881	$922.89	$922.95	$922.80