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	$64.71	7.222%	$69.3834	$69.38	$69.40	$69.40
Purchase #2	$35.39	12.512%	$39.818	$39.82	$39.80	$39.80
Purchase #3	$55.73	8.439%	$60.4331	$60.43	$60.45	$60.40
Purchase #4	$29.53	3.640%	$30.6049	$30.60	$30.60	$30.60
Purchase #5	$200.70	4.210%	$209.1495	$209.15	$209.15	$209.10
Purchase #6	$143.46	11.487%	$159.9393	$159.94	$159.95	$159.90
Purchase #7	$78.92	13.534%	$89.601	$89.60	$89.60	$89.60
7 purchase totals =	$608.44		$658.9292	$658.92	$658.95	$658.80