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	$225.30	11.282%	$250.7183	$250.72	$250.70	$250.70
Purchase #2	$203.69	12.167%	$228.473	$228.47	$228.45	$228.50
Purchase #3	$144.69	12.580%	$162.892	$162.89	$162.90	$162.90
Purchase #4	$16.62	13.190%	$18.8122	$18.81	$18.80	$18.80
Purchase #5	$17.89	7.171%	$19.1729	$19.17	$19.15	$19.20
Purchase #6	$240.90	9.208%	$263.0821	$263.08	$263.10	$263.10
Purchase #7	$54.36	6.283%	$57.7754	$57.78	$57.80	$57.80
7 purchase totals =	$903.45		$1,000.9259	$1,000.92	$1,000.90	$1,001.00