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	$160.58	6.694%	$171.3292	$171.33	$171.35	$171.30
Purchase #2	$18.72	8.805%	$20.3683	$20.37	$20.35	$20.40
Purchase #3	$141.72	4.788%	$148.5056	$148.51	$148.50	$148.50
Purchase #4	$81.54	5.639%	$86.138	$86.14	$86.15	$86.10
Purchase #5	$76.80	7.824%	$82.8088	$82.81	$82.80	$82.80
Purchase #6	$222.28	4.694%	$232.7138	$232.71	$232.70	$232.70
Purchase #7	$164.54	4.553%	$172.0315	$172.03	$172.05	$172.00
7 purchase totals =	$866.18		$913.8952	$913.90	$913.90	$913.80