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	$187.36	12.465%	$210.7144	$210.71	$210.70	$210.70
Purchase #2	$126.44	12.359%	$142.0667	$142.07	$142.05	$142.10
Purchase #3	$207.50	7.110%	$222.2533	$222.25	$222.25	$222.30
Purchase #4	$133.34	4.782%	$139.7163	$139.72	$139.70	$139.70
Purchase #5	$100.61	7.675%	$108.3318	$108.33	$108.35	$108.30
Purchase #6	$216.64	12.429%	$243.5662	$243.57	$243.55	$243.60
Purchase #7	$101.92	3.524%	$105.5117	$105.51	$105.50	$105.50
7 purchase totals =	$1,073.81		$1,172.1604	$1,172.16	$1,172.10	$1,172.20