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	$144.41	10.171%	$159.0979	$159.10	$159.10	$159.10
Purchase #2	$226.37	6.701%	$241.5391	$241.54	$241.55	$241.50
Purchase #3	$127.63	9.108%	$139.2545	$139.25	$139.25	$139.30
Purchase #4	$152.88	3.807%	$158.7001	$158.70	$158.70	$158.70
Purchase #5	$201.92	3.144%	$208.2684	$208.27	$208.25	$208.30
Purchase #6	$73.98	13.260%	$83.7897	$83.79	$83.80	$83.80
Purchase #7	$165.53	10.518%	$182.9404	$182.94	$182.95	$182.90
7 purchase totals =	$1,092.72		$1,173.5901	$1,173.59	$1,173.60	$1,173.60