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	$240.39	12.795%	$271.1479	$271.15	$271.15	$271.10
Purchase #2	$6.61	7.263%	$7.0901	$7.09	$7.10	$7.10
Purchase #3	$151.71	10.547%	$167.7109	$167.71	$167.70	$167.70
Purchase #4	$172.42	10.122%	$189.8724	$189.87	$189.85	$189.90
Purchase #5	$57.91	13.120%	$65.5078	$65.51	$65.50	$65.50
Purchase #6	$213.41	7.111%	$228.5856	$228.59	$228.60	$228.60
Purchase #7	$189.80	3.387%	$196.2285	$196.23	$196.25	$196.20
7 purchase totals =	$1,032.25		$1,126.1432	$1,126.15	$1,126.15	$1,126.10