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	$27.88	3.432%	$28.8368	$28.84	$28.85	$28.80
Purchase #2	$195.72	11.756%	$218.7288	$218.73	$218.75	$218.70
Purchase #3	$88.67	12.739%	$99.9657	$99.97	$99.95	$100.00
Purchase #4	$195.64	13.560%	$222.1688	$222.17	$222.15	$222.20
Purchase #5	$82.46	3.788%	$85.5836	$85.58	$85.60	$85.60
Purchase #6	$240.87	6.260%	$255.9485	$255.95	$255.95	$255.90
Purchase #7	$129.46	11.227%	$143.9945	$143.99	$144.00	$144.00
7 purchase totals =	$960.70		$1,055.2267	$1,055.23	$1,055.25	$1,055.20