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	$222.79	12.115%	$249.781	$249.78	$249.80	$249.80
Purchase #2	$241.50	4.861%	$253.2393	$253.24	$253.25	$253.20
Purchase #3	$54.58	11.235%	$60.7121	$60.71	$60.70	$60.70
Purchase #4	$94.88	6.216%	$100.7777	$100.78	$100.80	$100.80
Purchase #5	$210.54	4.139%	$219.2543	$219.25	$219.25	$219.30
Purchase #6	$38.30	13.144%	$43.3342	$43.33	$43.35	$43.30
Purchase #7	$108.59	13.764%	$123.5363	$123.54	$123.55	$123.50
7 purchase totals =	$971.18		$1,050.6349	$1,050.63	$1,050.70	$1,050.60