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	$123.51	8.172%	$133.6032	$133.60	$133.60	$133.60
Purchase #2	$237.52	11.305%	$264.3716	$264.37	$264.35	$264.40
Purchase #3	$22.68	8.257%	$24.5527	$24.55	$24.55	$24.60
Purchase #4	$69.60	4.274%	$72.5747	$72.57	$72.55	$72.60
Purchase #5	$211.97	12.709%	$238.9093	$238.91	$238.90	$238.90
Purchase #6	$91.32	9.151%	$99.6767	$99.68	$99.70	$99.70
Purchase #7	$227.98	8.434%	$247.2078	$247.21	$247.20	$247.20
7 purchase totals =	$984.58		$1,080.8960	$1,080.89	$1,080.85	$1,081.00