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	$94.44	6.429%	$100.5115	$100.51	$100.50	$100.50
Purchase #2	$232.38	5.243%	$244.5637	$244.56	$244.55	$244.60
Purchase #3	$79.68	12.704%	$89.8025	$89.80	$89.80	$89.80
Purchase #4	$70.29	9.400%	$76.8973	$76.90	$76.90	$76.90
Purchase #5	$17.68	12.468%	$19.8843	$19.88	$19.90	$19.90
Purchase #6	$169.98	11.576%	$189.6569	$189.66	$189.65	$189.70
Purchase #7	$99.30	5.291%	$104.554	$104.55	$104.55	$104.60
7 purchase totals =	$763.75		$825.8702	$825.86	$825.85	$826.00