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	$140.27	13.790%	$159.6132	$159.61	$159.60	$159.60
Purchase #2	$107.27	5.693%	$113.3769	$113.38	$113.40	$113.40
Purchase #3	$19.81	13.805%	$22.5448	$22.54	$22.55	$22.50
Purchase #4	$93.91	11.544%	$104.751	$104.75	$104.75	$104.80
Purchase #5	$185.81	13.173%	$210.2868	$210.29	$210.30	$210.30
Purchase #6	$49.60	11.664%	$55.3853	$55.39	$55.40	$55.40
Purchase #7	$6.86	9.468%	$7.5095	$7.51	$7.50	$7.50
7 purchase totals =	$603.53		$673.4675	$673.47	$673.50	$673.50