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	$75.27	12.152%	$84.4168	$84.42	$84.40	$84.40
Purchase #2	$130.91	9.648%	$143.5402	$143.54	$143.55	$143.50
Purchase #3	$72.41	6.256%	$76.94	$76.94	$76.95	$76.90
Purchase #4	$83.80	13.272%	$94.9219	$94.92	$94.90	$94.90
Purchase #5	$164.89	8.871%	$179.5174	$179.52	$179.50	$179.50
Purchase #6	$242.81	11.387%	$270.4588	$270.46	$270.45	$270.50
Purchase #7	$67.56	3.806%	$70.1313	$70.13	$70.15	$70.10
7 purchase totals =	$837.65		$919.9264	$919.93	$919.90	$919.80