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	$190.71	5.299%	$200.8157	$200.82	$200.80	$200.80
Purchase #2	$135.30	7.411%	$145.3271	$145.33	$145.35	$145.30
Purchase #3	$73.50	11.537%	$81.9797	$81.98	$82.00	$82.00
Purchase #4	$10.43	3.150%	$10.7585	$10.76	$10.75	$10.80
Purchase #5	$83.67	6.840%	$89.393	$89.39	$89.40	$89.40
Purchase #6	$8.27	10.297%	$9.1216	$9.12	$9.10	$9.10
Purchase #7	$245.52	13.431%	$278.4958	$278.50	$278.50	$278.50
7 purchase totals =	$747.40		$815.8914	$815.90	$815.90	$815.90