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	$83.88	7.253%	$89.9638	$89.96	$89.95	$90.00
Purchase #2	$20.34	7.447%	$21.8547	$21.85	$21.85	$21.90
Purchase #3	$17.65	4.178%	$18.3874	$18.39	$18.40	$18.40
Purchase #4	$245.95	9.447%	$269.1849	$269.18	$269.20	$269.20
Purchase #5	$23.99	13.146%	$27.1437	$27.14	$27.15	$27.10
Purchase #6	$174.43	12.118%	$195.5674	$195.57	$195.55	$195.60
Purchase #7	$140.89	6.517%	$150.0718	$150.07	$150.05	$150.10
7 purchase totals =	$707.13		$772.1737	$772.16	$772.15	$772.30