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	$96.99	5.667%	$102.4864	$102.49	$102.50	$102.50
Purchase #2	$213.72	11.317%	$237.9067	$237.91	$237.90	$237.90
Purchase #3	$74.33	12.711%	$83.7781	$83.78	$83.80	$83.80
Purchase #4	$18.91	8.282%	$20.4761	$20.48	$20.50	$20.50
Purchase #5	$185.33	13.602%	$210.5386	$210.54	$210.55	$210.50
Purchase #6	$172.49	5.781%	$182.4616	$182.46	$182.45	$182.50
Purchase #7	$223.43	12.564%	$251.5017	$251.50	$251.50	$251.50
7 purchase totals =	$985.20		$1,089.1492	$1,089.16	$1,089.20	$1,089.20