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	$239.39	3.141%	$246.9092	$246.91	$246.90	$246.90
Purchase #2	$235.33	5.242%	$247.666	$247.67	$247.65	$247.70
Purchase #3	$6.43	13.799%	$7.3173	$7.32	$7.30	$7.30
Purchase #4	$50.28	11.201%	$55.9119	$55.91	$55.90	$55.90
Purchase #5	$93.27	6.264%	$99.1124	$99.11	$99.10	$99.10
Purchase #6	$192.30	12.600%	$216.5298	$216.53	$216.55	$216.50
Purchase #7	$244.76	13.680%	$278.2432	$278.24	$278.25	$278.20
7 purchase totals =	$1,061.76		$1,151.6898	$1,151.69	$1,151.65	$1,151.60