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	$7.52	8.509%	$8.1599	$8.16	$8.15	$8.20
Purchase #2	$192.25	4.358%	$200.6283	$200.63	$200.65	$200.60
Purchase #3	$82.63	8.526%	$89.675	$89.68	$89.70	$89.70
Purchase #4	$152.29	11.232%	$169.3952	$169.40	$169.40	$169.40
Purchase #5	$211.60	9.362%	$231.41	$231.41	$231.40	$231.40
Purchase #6	$65.56	9.492%	$71.783	$71.78	$71.80	$71.80
Purchase #7	$144.65	6.665%	$154.2909	$154.29	$154.30	$154.30
7 purchase totals =	$856.50		$925.3423	$925.35	$925.40	$925.40