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	$26.40	12.157%	$29.6094	$29.61	$29.60	$29.60
Purchase #2	$219.53	10.350%	$242.2514	$242.25	$242.25	$242.30
Purchase #3	$158.87	8.469%	$172.3247	$172.32	$172.30	$172.30
Purchase #4	$133.66	6.790%	$142.7355	$142.74	$142.75	$142.70
Purchase #5	$46.88	10.745%	$51.9173	$51.92	$51.90	$51.90
Purchase #6	$66.90	6.686%	$71.3729	$71.37	$71.35	$71.40
Purchase #7	$78.55	9.279%	$85.8387	$85.84	$85.85	$85.80
7 purchase totals =	$730.79		$796.0499	$796.05	$796.00	$796.00