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	$125.40	9.678%	$137.5362	$137.54	$137.55	$137.50
Purchase #2	$172.76	4.832%	$181.1078	$181.11	$181.10	$181.10
Purchase #3	$146.91	3.144%	$151.5289	$151.53	$151.55	$151.50
Purchase #4	$104.79	3.303%	$108.2512	$108.25	$108.25	$108.30
Purchase #5	$33.29	12.603%	$37.4855	$37.49	$37.50	$37.50
Purchase #6	$88.37	7.616%	$95.1003	$95.10	$95.10	$95.10
Purchase #7	$156.90	7.728%	$169.0252	$169.03	$169.05	$169.00
7 purchase totals =	$828.42		$880.0351	$880.05	$880.10	$880.00