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	$112.73	13.275%	$127.6949	$127.69	$127.70	$127.70
Purchase #2	$123.44	8.134%	$133.4806	$133.48	$133.50	$133.50
Purchase #3	$86.61	9.549%	$94.8804	$94.88	$94.90	$94.90
Purchase #4	$65.45	3.618%	$67.818	$67.82	$67.80	$67.80
Purchase #5	$190.80	9.731%	$209.3667	$209.37	$209.35	$209.40
Purchase #6	$52.72	9.268%	$57.6061	$57.61	$57.60	$57.60
Purchase #7	$45.78	8.271%	$49.5665	$49.57	$49.55	$49.60
7 purchase totals =	$677.53		$740.4132	$740.42	$740.40	$740.50