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	$215.56	7.310%	$231.3174	$231.32	$231.30	$231.30
Purchase #2	$192.45	3.175%	$198.5603	$198.56	$198.55	$198.60
Purchase #3	$244.31	8.132%	$264.1773	$264.18	$264.20	$264.20
Purchase #4	$135.99	10.755%	$150.6157	$150.62	$150.60	$150.60
Purchase #5	$234.44	3.517%	$242.6853	$242.69	$242.70	$242.70
Purchase #6	$88.85	11.462%	$99.034	$99.03	$99.05	$99.00
Purchase #7	$82.29	8.640%	$89.3999	$89.40	$89.40	$89.40
7 purchase totals =	$1,193.89		$1,275.7899	$1,275.80	$1,275.80	$1,275.80