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	$6.74	11.578%	$7.5204	$7.52	$7.50	$7.50
Purchase #2	$33.92	6.126%	$35.9979	$36.00	$36.00	$36.00
Purchase #3	$43.47	8.621%	$47.2175	$47.22	$47.20	$47.20
Purchase #4	$161.54	11.683%	$180.4127	$180.41	$180.40	$180.40
Purchase #5	$141.59	7.772%	$152.5944	$152.59	$152.60	$152.60
Purchase #6	$102.59	11.427%	$114.313	$114.31	$114.30	$114.30
Purchase #7	$193.64	11.267%	$215.4574	$215.46	$215.45	$215.50
7 purchase totals =	$683.49		$753.5133	$753.51	$753.45	$753.50