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	$81.33	10.655%	$89.9957	$90.00	$90.00	$90.00
Purchase #2	$57.92	5.866%	$61.3176	$61.32	$61.30	$61.30
Purchase #3	$51.99	3.681%	$53.9038	$53.90	$53.90	$53.90
Purchase #4	$61.64	5.308%	$64.9119	$64.91	$64.90	$64.90
Purchase #5	$115.74	9.137%	$126.3152	$126.32	$126.30	$126.30
Purchase #6	$139.62	12.117%	$156.5378	$156.54	$156.55	$156.50
Purchase #7	$103.50	6.537%	$110.2658	$110.27	$110.25	$110.30
7 purchase totals =	$611.74		$663.2478	$663.26	$663.20	$663.20