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	$122.83	3.509%	$127.1401	$127.14	$127.15	$127.10
Purchase #2	$152.90	4.718%	$160.1138	$160.11	$160.10	$160.10
Purchase #3	$42.64	13.306%	$48.3137	$48.31	$48.30	$48.30
Purchase #4	$170.67	3.345%	$176.3789	$176.38	$176.40	$176.40
Purchase #5	$93.48	6.382%	$99.4459	$99.45	$99.45	$99.40
Purchase #6	$138.26	13.515%	$156.9458	$156.95	$156.95	$156.90
Purchase #7	$116.53	13.765%	$132.5704	$132.57	$132.55	$132.60
7 purchase totals =	$837.31		$900.9086	$900.91	$900.90	$900.80