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	$92.84	12.811%	$104.7337	$104.73	$104.75	$104.70
Purchase #2	$13.31	4.817%	$13.9511	$13.95	$13.95	$14.00
Purchase #3	$53.61	11.538%	$59.7955	$59.80	$59.80	$59.80
Purchase #4	$124.46	11.843%	$139.1998	$139.20	$139.20	$139.20
Purchase #5	$250.47	10.513%	$276.8019	$276.80	$276.80	$276.80
Purchase #6	$99.68	11.768%	$111.4103	$111.41	$111.40	$111.40
Purchase #7	$27.93	10.467%	$30.8534	$30.85	$30.85	$30.90
7 purchase totals =	$662.30		$736.7457	$736.74	$736.75	$736.80