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	$121.89	7.555%	$131.0988	$131.10	$131.10	$131.10
Purchase #2	$91.86	11.549%	$102.4689	$102.47	$102.45	$102.50
Purchase #3	$17.56	11.658%	$19.6071	$19.61	$19.60	$19.60
Purchase #4	$81.60	5.122%	$85.7796	$85.78	$85.80	$85.80
Purchase #5	$243.65	3.624%	$252.4799	$252.48	$252.50	$252.50
Purchase #6	$106.63	11.268%	$118.6451	$118.65	$118.65	$118.60
Purchase #7	$245.86	11.633%	$274.4609	$274.46	$274.45	$274.50
7 purchase totals =	$909.05		$984.5403	$984.55	$984.55	$984.60