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	$189.83	5.609%	$200.4776	$200.48	$200.50	$200.50
Purchase #2	$5.26	10.286%	$5.801	$5.80	$5.80	$5.80
Purchase #3	$51.56	13.668%	$58.6072	$58.61	$58.60	$58.60
Purchase #4	$6.66	12.643%	$7.502	$7.50	$7.50	$7.50
Purchase #5	$79.30	13.674%	$90.1435	$90.14	$90.15	$90.10
Purchase #6	$151.90	4.642%	$158.9512	$158.95	$158.95	$159.00
Purchase #7	$17.94	13.322%	$20.33	$20.33	$20.35	$20.30
7 purchase totals =	$502.45		$541.8125	$541.81	$541.85	$541.80