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	$139.68	7.757%	$150.515	$150.52	$150.50	$150.50
Purchase #2	$36.79	12.301%	$41.3155	$41.32	$41.30	$41.30
Purchase #3	$167.77	7.841%	$180.9248	$180.92	$180.90	$180.90
Purchase #4	$248.82	10.209%	$274.222	$274.22	$274.20	$274.20
Purchase #5	$75.86	4.193%	$79.0408	$79.04	$79.05	$79.00
Purchase #6	$97.34	8.705%	$105.8134	$105.81	$105.80	$105.80
Purchase #7	$153.89	11.575%	$171.7028	$171.70	$171.70	$171.70
7 purchase totals =	$920.15		$1,003.5343	$1,003.53	$1,003.45	$1,003.40