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	$137.66	13.392%	$156.0954	$156.10	$156.10	$156.10
Purchase #2	$165.99	13.426%	$188.2758	$188.28	$188.30	$188.30
Purchase #3	$133.83	9.557%	$146.6201	$146.62	$146.60	$146.60
Purchase #4	$216.61	3.783%	$224.8044	$224.80	$224.80	$224.80
Purchase #5	$95.32	11.145%	$105.9434	$105.94	$105.95	$105.90
Purchase #6	$229.41	6.313%	$243.8927	$243.89	$243.90	$243.90
Purchase #7	$196.87	3.416%	$203.5951	$203.60	$203.60	$203.60
7 purchase totals =	$1,175.69		$1,269.2269	$1,269.23	$1,269.25	$1,269.20