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	$72.65	9.363%	$79.4522	$79.45	$79.45	$79.50
Purchase #2	$169.92	10.201%	$187.2535	$187.25	$187.25	$187.30
Purchase #3	$162.54	3.708%	$168.567	$168.57	$168.55	$168.60
Purchase #4	$65.32	11.657%	$72.9344	$72.93	$72.95	$72.90
Purchase #5	$181.35	3.391%	$187.4996	$187.50	$187.50	$187.50
Purchase #6	$166.46	4.865%	$174.5583	$174.56	$174.55	$174.60
Purchase #7	$92.51	3.547%	$95.7913	$95.79	$95.80	$95.80
7 purchase totals =	$910.75		$966.0563	$966.05	$966.05	$966.20