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	$76.69	8.785%	$83.4272	$83.43	$83.45	$83.40
Purchase #2	$123.87	6.242%	$131.602	$131.60	$131.60	$131.60
Purchase #3	$82.81	8.482%	$89.8339	$89.83	$89.85	$89.80
Purchase #4	$153.91	11.591%	$171.7497	$171.75	$171.75	$171.70
Purchase #5	$165.35	11.374%	$184.1569	$184.16	$184.15	$184.20
Purchase #6	$9.69	5.816%	$10.2536	$10.25	$10.25	$10.30
Purchase #7	$82.42	8.380%	$89.3268	$89.33	$89.35	$89.30
7 purchase totals =	$694.74		$760.3501	$760.35	$760.40	$760.30