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	$83.99	7.654%	$90.4186	$90.42	$90.40	$90.40
Purchase #2	$45.28	4.178%	$47.1718	$47.17	$47.15	$47.20
Purchase #3	$232.57	7.205%	$249.3267	$249.33	$249.35	$249.30
Purchase #4	$16.37	10.273%	$18.0517	$18.05	$18.05	$18.10
Purchase #5	$140.48	3.605%	$145.5443	$145.54	$145.55	$145.50
Purchase #6	$141.70	3.273%	$146.3378	$146.34	$146.35	$146.30
Purchase #7	$89.33	7.322%	$95.8707	$95.87	$95.85	$95.90
7 purchase totals =	$749.72		$792.7216	$792.72	$792.70	$792.70