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	$35.48	7.529%	$38.1513	$38.15	$38.15	$38.20
Purchase #2	$113.67	9.408%	$124.3641	$124.36	$124.35	$124.40
Purchase #3	$90.82	10.565%	$100.4151	$100.42	$100.40	$100.40
Purchase #4	$72.59	12.323%	$81.5353	$81.54	$81.55	$81.50
Purchase #5	$205.39	8.761%	$223.3842	$223.38	$223.40	$223.40
Purchase #6	$136.31	11.146%	$151.5031	$151.50	$151.50	$151.50
Purchase #7	$30.89	11.845%	$34.5489	$34.55	$34.55	$34.50
7 purchase totals =	$685.15		$753.9020	$753.90	$753.90	$753.90