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	$142.82	5.511%	$150.6908	$150.69	$150.70	$150.70
Purchase #2	$38.77	4.528%	$40.5255	$40.53	$40.55	$40.50
Purchase #3	$108.69	12.845%	$122.6512	$122.65	$122.65	$122.70
Purchase #4	$86.38	3.744%	$89.6141	$89.61	$89.60	$89.60
Purchase #5	$83.41	5.668%	$88.1377	$88.14	$88.15	$88.10
Purchase #6	$65.55	12.864%	$73.9824	$73.98	$74.00	$74.00
Purchase #7	$196.58	11.248%	$218.6913	$218.69	$218.70	$218.70
7 purchase totals =	$722.20		$784.2930	$784.29	$784.35	$784.30