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	$153.90	11.295%	$171.283	$171.28	$171.30	$171.30
Purchase #2	$239.77	4.568%	$250.7227	$250.72	$250.70	$250.70
Purchase #3	$123.72	7.545%	$133.0547	$133.05	$133.05	$133.10
Purchase #4	$83.38	11.401%	$92.8862	$92.89	$92.90	$92.90
Purchase #5	$53.89	5.280%	$56.7354	$56.74	$56.75	$56.70
Purchase #6	$83.61	12.602%	$94.1465	$94.15	$94.15	$94.10
Purchase #7	$58.51	6.251%	$62.1675	$62.17	$62.15	$62.20
7 purchase totals =	$796.78		$860.9960	$861.00	$861.00	$861.00