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	$80.61	11.216%	$89.6512	$89.65	$89.65	$89.70
Purchase #2	$234.63	12.405%	$263.7359	$263.74	$263.75	$263.70
Purchase #3	$157.72	12.358%	$177.211	$177.21	$177.20	$177.20
Purchase #4	$59.83	6.557%	$63.7531	$63.75	$63.75	$63.80
Purchase #5	$48.32	12.488%	$54.3542	$54.35	$54.35	$54.40
Purchase #6	$28.88	12.437%	$32.4718	$32.47	$32.45	$32.50
Purchase #7	$158.39	4.501%	$165.5191	$165.52	$165.50	$165.50
7 purchase totals =	$768.38		$846.6963	$846.69	$846.65	$846.80