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	$122.77	9.846%	$134.8579	$134.86	$134.85	$134.90
Purchase #2	$123.54	9.595%	$135.3937	$135.39	$135.40	$135.40
Purchase #3	$183.98	11.351%	$204.8636	$204.86	$204.85	$204.90
Purchase #4	$195.40	6.612%	$208.3198	$208.32	$208.30	$208.30
Purchase #5	$70.60	3.237%	$72.8853	$72.89	$72.90	$72.90
Purchase #6	$184.80	8.596%	$200.6854	$200.69	$200.70	$200.70
Purchase #7	$98.25	13.133%	$111.1532	$111.15	$111.15	$111.20
7 purchase totals =	$979.34		$1,068.1589	$1,068.16	$1,068.15	$1,068.30