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	$52.81	12.614%	$59.4715	$59.47	$59.45	$59.50
Purchase #2	$218.79	7.717%	$235.674	$235.67	$235.65	$235.70
Purchase #3	$177.70	4.477%	$185.6556	$185.66	$185.65	$185.70
Purchase #4	$31.57	12.386%	$35.4803	$35.48	$35.50	$35.50
Purchase #5	$116.74	8.603%	$126.7831	$126.78	$126.80	$126.80
Purchase #6	$106.84	12.818%	$120.5348	$120.53	$120.55	$120.50
Purchase #7	$113.96	11.868%	$127.4848	$127.48	$127.50	$127.50
7 purchase totals =	$818.41		$891.0841	$891.07	$891.10	$891.20