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	$12.87	13.739%	$14.6382	$14.64	$14.65	$14.60
Purchase #2	$60.50	11.681%	$67.567	$67.57	$67.55	$67.60
Purchase #3	$51.69	10.765%	$57.2544	$57.25	$57.25	$57.30
Purchase #4	$210.40	11.132%	$233.8217	$233.82	$233.80	$233.80
Purchase #5	$209.47	4.874%	$219.6796	$219.68	$219.70	$219.70
Purchase #6	$140.29	5.835%	$148.4759	$148.48	$148.50	$148.50
Purchase #7	$161.37	11.813%	$180.4326	$180.43	$180.45	$180.40
7 purchase totals =	$846.59		$921.8694	$921.87	$921.90	$921.90