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	$90.88	13.105%	$102.7898	$102.79	$102.80	$102.80
Purchase #2	$80.62	11.151%	$89.6099	$89.61	$89.60	$89.60
Purchase #3	$78.66	12.413%	$88.4241	$88.42	$88.40	$88.40
Purchase #4	$248.59	8.335%	$269.31	$269.31	$269.30	$269.30
Purchase #5	$173.98	10.310%	$191.9173	$191.92	$191.90	$191.90
Purchase #6	$8.46	12.728%	$9.5368	$9.54	$9.55	$9.50
Purchase #7	$114.83	12.297%	$128.9506	$128.95	$128.95	$129.00
7 purchase totals =	$796.02		$880.5385	$880.54	$880.50	$880.50