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	$18.26	10.646%	$20.204	$20.20	$20.20	$20.20
Purchase #2	$165.70	3.248%	$171.0819	$171.08	$171.10	$171.10
Purchase #3	$40.26	11.195%	$44.7671	$44.77	$44.75	$44.80
Purchase #4	$59.37	9.744%	$65.155	$65.16	$65.15	$65.20
Purchase #5	$57.40	3.360%	$59.3286	$59.33	$59.35	$59.30
Purchase #6	$171.56	9.689%	$188.1824	$188.18	$188.20	$188.20
Purchase #7	$46.95	10.841%	$52.0398	$52.04	$52.05	$52.00
7 purchase totals =	$559.50		$600.7588	$600.76	$600.80	$600.80