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	$17.28	6.377%	$18.3819	$18.38	$18.40	$18.40
Purchase #2	$120.28	9.590%	$131.8149	$131.81	$131.80	$131.80
Purchase #3	$178.91	7.179%	$191.7539	$191.75	$191.75	$191.80
Purchase #4	$63.58	5.453%	$67.047	$67.05	$67.05	$67.00
Purchase #5	$61.97	12.657%	$69.8135	$69.81	$69.80	$69.80
Purchase #6	$153.87	11.449%	$171.4866	$171.49	$171.50	$171.50
Purchase #7	$96.27	3.303%	$99.4498	$99.45	$99.45	$99.40
7 purchase totals =	$692.16		$749.7476	$749.74	$749.75	$749.70