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	$165.71	8.517%	$179.8235	$179.82	$179.80	$179.80
Purchase #2	$28.35	13.527%	$32.1849	$32.18	$32.20	$32.20
Purchase #3	$18.98	4.389%	$19.813	$19.81	$19.80	$19.80
Purchase #4	$59.96	11.765%	$67.0143	$67.01	$67.00	$67.00
Purchase #5	$90.41	9.649%	$99.1337	$99.13	$99.15	$99.10
Purchase #6	$147.89	13.871%	$168.4038	$168.40	$168.40	$168.40
Purchase #7	$68.94	12.152%	$77.3176	$77.32	$77.30	$77.30
7 purchase totals =	$580.24		$643.6908	$643.67	$643.65	$643.60