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	$148.82	5.637%	$157.209	$157.21	$157.20	$157.20
Purchase #2	$86.64	4.766%	$90.7693	$90.77	$90.75	$90.80
Purchase #3	$72.95	4.239%	$76.0424	$76.04	$76.05	$76.00
Purchase #4	$81.43	9.135%	$88.8686	$88.87	$88.85	$88.90
Purchase #5	$197.85	12.870%	$223.3133	$223.31	$223.30	$223.30
Purchase #6	$127.29	7.494%	$136.8291	$136.83	$136.85	$136.80
Purchase #7	$159.73	5.122%	$167.9114	$167.91	$167.90	$167.90
7 purchase totals =	$874.71		$940.9431	$940.94	$940.90	$940.90