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	$33.29	6.338%	$35.3999	$35.40	$35.40	$35.40
Purchase #2	$250.72	8.783%	$272.7407	$272.74	$272.75	$272.70
Purchase #3	$187.44	12.356%	$210.6001	$210.60	$210.60	$210.60
Purchase #4	$194.90	10.559%	$215.4795	$215.48	$215.50	$215.50
Purchase #5	$90.38	7.196%	$96.8837	$96.88	$96.90	$96.90
Purchase #6	$51.93	11.191%	$57.7415	$57.74	$57.75	$57.70
Purchase #7	$40.61	12.810%	$45.8121	$45.81	$45.80	$45.80
7 purchase totals =	$849.27		$934.6575	$934.65	$934.70	$934.60