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	$109.95	9.275%	$120.1479	$120.15	$120.15	$120.10
Purchase #2	$152.44	10.477%	$168.4111	$168.41	$168.40	$168.40
Purchase #3	$123.85	8.144%	$133.9363	$133.94	$133.95	$133.90
Purchase #4	$67.52	7.439%	$72.5428	$72.54	$72.55	$72.50
Purchase #5	$130.74	12.522%	$147.1113	$147.11	$147.10	$147.10
Purchase #6	$69.72	13.324%	$79.0095	$79.01	$79.00	$79.00
Purchase #7	$94.64	5.226%	$99.5859	$99.59	$99.60	$99.60
7 purchase totals =	$748.86		$820.7448	$820.75	$820.75	$820.60