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	$76.84	6.160%	$81.5733	$81.57	$81.55	$81.60
Purchase #2	$38.54	13.757%	$43.8419	$43.84	$43.85	$43.80
Purchase #3	$29.81	12.656%	$33.5828	$33.58	$33.60	$33.60
Purchase #4	$88.28	7.228%	$94.6609	$94.66	$94.65	$94.70
Purchase #5	$70.66	4.601%	$73.9111	$73.91	$73.90	$73.90
Purchase #6	$133.64	12.690%	$150.5989	$150.60	$150.60	$150.60
Purchase #7	$39.69	5.809%	$41.9956	$42.00	$42.00	$42.00
7 purchase totals =	$477.46		$520.1645	$520.16	$520.15	$520.20