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	$90.45	10.436%	$99.8894	$99.89	$99.90	$99.90
Purchase #2	$191.69	5.832%	$202.8694	$202.87	$202.85	$202.90
Purchase #3	$126.46	6.665%	$134.8886	$134.89	$134.90	$134.90
Purchase #4	$185.46	5.234%	$195.167	$195.17	$195.15	$195.20
Purchase #5	$65.38	10.361%	$72.154	$72.15	$72.15	$72.20
Purchase #6	$180.89	8.420%	$196.1209	$196.12	$196.10	$196.10
Purchase #7	$248.82	11.442%	$277.29	$277.29	$277.30	$277.30
7 purchase totals =	$1,089.15		$1,178.3793	$1,178.38	$1,178.35	$1,178.50