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	$126.80	8.625%	$137.7365	$137.74	$137.75	$137.70
Purchase #2	$106.59	11.703%	$119.0642	$119.06	$119.05	$119.10
Purchase #3	$104.59	4.414%	$109.2066	$109.21	$109.20	$109.20
Purchase #4	$9.92	13.749%	$11.2839	$11.28	$11.30	$11.30
Purchase #5	$90.89	9.463%	$99.4909	$99.49	$99.50	$99.50
Purchase #6	$59.40	13.130%	$67.1992	$67.20	$67.20	$67.20
Purchase #7	$250.93	5.454%	$264.6157	$264.62	$264.60	$264.60
7 purchase totals =	$749.12		$808.5970	$808.60	$808.60	$808.60