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	$78.72	4.344%	$82.1396	$82.14	$82.15	$82.10
Purchase #2	$157.91	7.848%	$170.3028	$170.30	$170.30	$170.30
Purchase #3	$14.95	7.453%	$16.0642	$16.06	$16.05	$16.10
Purchase #4	$215.58	10.454%	$238.1167	$238.12	$238.10	$238.10
Purchase #5	$159.46	13.748%	$181.3826	$181.38	$181.40	$181.40
Purchase #6	$80.42	7.656%	$86.577	$86.58	$86.60	$86.60
Purchase #7	$128.97	9.254%	$140.9049	$140.90	$140.90	$140.90
7 purchase totals =	$836.01		$915.4878	$915.48	$915.50	$915.50