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	$29.67	10.231%	$32.7055	$32.71	$32.70	$32.70
Purchase #2	$191.52	4.382%	$199.9124	$199.91	$199.90	$199.90
Purchase #3	$114.29	11.846%	$127.8288	$127.83	$127.85	$127.80
Purchase #4	$33.74	8.485%	$36.6028	$36.60	$36.60	$36.60
Purchase #5	$149.97	12.184%	$168.2423	$168.24	$168.25	$168.20
Purchase #6	$55.86	3.799%	$57.9821	$57.98	$58.00	$58.00
Purchase #7	$42.75	11.140%	$47.5124	$47.51	$47.50	$47.50
7 purchase totals =	$617.80		$670.7863	$670.78	$670.80	$670.70