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	$6.92	13.693%	$7.8676	$7.87	$7.85	$7.90
Purchase #2	$131.54	3.474%	$136.1097	$136.11	$136.10	$136.10
Purchase #3	$110.88	6.856%	$118.4819	$118.48	$118.50	$118.50
Purchase #4	$45.76	10.832%	$50.7167	$50.72	$50.70	$50.70
Purchase #5	$154.51	11.689%	$172.5707	$172.57	$172.55	$172.60
Purchase #6	$29.97	10.825%	$33.2143	$33.21	$33.20	$33.20
Purchase #7	$205.91	8.765%	$223.958	$223.96	$223.95	$224.00
7 purchase totals =	$685.49		$742.9189	$742.92	$742.85	$743.00