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	$241.33	10.442%	$266.5297	$266.53	$266.55	$266.50
Purchase #2	$104.62	6.604%	$111.5291	$111.53	$111.55	$111.50
Purchase #3	$164.74	9.834%	$180.9405	$180.94	$180.95	$180.90
Purchase #4	$59.63	5.310%	$62.7964	$62.80	$62.80	$62.80
Purchase #5	$33.37	12.578%	$37.5673	$37.57	$37.55	$37.60
Purchase #6	$146.73	5.532%	$154.8471	$154.85	$154.85	$154.80
Purchase #7	$67.89	11.126%	$75.4434	$75.44	$75.45	$75.40
7 purchase totals =	$818.31		$889.6535	$889.66	$889.70	$889.50