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	$32.51	10.728%	$35.9977	$36.00	$36.00	$36.00
Purchase #2	$179.91	12.406%	$202.2296	$202.23	$202.25	$202.20
Purchase #3	$77.64	10.827%	$86.0461	$86.05	$86.05	$86.00
Purchase #4	$33.61	11.575%	$37.5004	$37.50	$37.50	$37.50
Purchase #5	$247.90	8.748%	$269.5863	$269.59	$269.60	$269.60
Purchase #6	$73.57	6.454%	$78.3182	$78.32	$78.30	$78.30
Purchase #7	$90.40	9.853%	$99.3071	$99.31	$99.30	$99.30
7 purchase totals =	$735.54		$808.9854	$809.00	$809.00	$808.90