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	$87.62	13.622%	$99.5556	$99.56	$99.55	$99.60
Purchase #2	$28.33	5.604%	$29.9176	$29.92	$29.90	$29.90
Purchase #3	$198.82	4.853%	$208.4687	$208.47	$208.45	$208.50
Purchase #4	$65.78	7.460%	$70.6872	$70.69	$70.70	$70.70
Purchase #5	$57.80	6.369%	$61.4813	$61.48	$61.50	$61.50
Purchase #6	$168.44	10.250%	$185.7051	$185.71	$185.70	$185.70
Purchase #7	$51.43	10.836%	$57.003	$57.00	$57.00	$57.00
7 purchase totals =	$658.22		$712.8185	$712.83	$712.80	$712.90