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	$68.77	5.471%	$72.5324	$72.53	$72.55	$72.50
Purchase #2	$41.26	10.835%	$45.7305	$45.73	$45.75	$45.70
Purchase #3	$121.37	10.774%	$134.4464	$134.45	$134.45	$134.40
Purchase #4	$200.85	4.779%	$210.4486	$210.45	$210.45	$210.40
Purchase #5	$97.69	11.365%	$108.7925	$108.79	$108.80	$108.80
Purchase #6	$149.74	11.682%	$167.2326	$167.23	$167.25	$167.20
Purchase #7	$50.94	6.818%	$54.4131	$54.41	$54.40	$54.40
7 purchase totals =	$730.62		$793.5961	$793.59	$793.65	$793.40