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	$249.52	11.531%	$278.2922	$278.29	$278.30	$278.30
Purchase #2	$155.89	12.662%	$175.6288	$175.63	$175.65	$175.60
Purchase #3	$213.77	4.250%	$222.8552	$222.86	$222.85	$222.90
Purchase #4	$81.75	11.469%	$91.1259	$91.13	$91.15	$91.10
Purchase #5	$76.25	12.669%	$85.9101	$85.91	$85.90	$85.90
Purchase #6	$200.98	10.686%	$222.4567	$222.46	$222.45	$222.50
Purchase #7	$76.59	11.861%	$85.6743	$85.67	$85.65	$85.70
7 purchase totals =	$1,054.75		$1,161.9432	$1,161.95	$1,161.95	$1,162.00