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	$56.94	7.445%	$61.1792	$61.18	$61.20	$61.20
Purchase #2	$89.73	10.657%	$99.2925	$99.29	$99.30	$99.30
Purchase #3	$126.31	12.715%	$142.3703	$142.37	$142.35	$142.40
Purchase #4	$89.76	11.626%	$100.1955	$100.20	$100.20	$100.20
Purchase #5	$101.50	11.682%	$113.3572	$113.36	$113.35	$113.40
Purchase #6	$189.68	6.229%	$201.4952	$201.50	$201.50	$201.50
Purchase #7	$121.88	5.460%	$128.5346	$128.53	$128.55	$128.50
7 purchase totals =	$775.80		$846.4245	$846.43	$846.45	$846.50