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	$234.54	3.497%	$242.7419	$242.74	$242.75	$242.70
Purchase #2	$110.59	11.322%	$123.111	$123.11	$123.10	$123.10
Purchase #3	$105.50	12.314%	$118.4913	$118.49	$118.50	$118.50
Purchase #4	$105.56	8.419%	$114.4471	$114.45	$114.45	$114.40
Purchase #5	$83.75	9.710%	$91.8821	$91.88	$91.90	$91.90
Purchase #6	$118.34	3.210%	$122.1387	$122.14	$122.15	$122.10
Purchase #7	$43.79	8.233%	$47.3952	$47.40	$47.40	$47.40
7 purchase totals =	$802.07		$860.2073	$860.21	$860.25	$860.10