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	$15.45	13.366%	$17.515	$17.52	$17.50	$17.50
Purchase #2	$77.75	9.546%	$85.172	$85.17	$85.15	$85.20
Purchase #3	$81.33	10.219%	$89.6411	$89.64	$89.65	$89.60
Purchase #4	$74.46	13.394%	$84.4332	$84.43	$84.45	$84.40
Purchase #5	$80.39	6.861%	$85.9056	$85.91	$85.90	$85.90
Purchase #6	$186.86	7.272%	$200.4485	$200.45	$200.45	$200.40
Purchase #7	$157.54	11.418%	$175.5279	$175.53	$175.55	$175.50
7 purchase totals =	$673.78		$738.6433	$738.65	$738.65	$738.50