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	$117.56	5.292%	$123.7813	$123.78	$123.80	$123.80
Purchase #2	$208.87	9.368%	$228.4369	$228.44	$228.45	$228.40
Purchase #3	$232.45	13.682%	$264.2538	$264.25	$264.25	$264.30
Purchase #4	$40.84	7.290%	$43.8172	$43.82	$43.80	$43.80
Purchase #5	$244.79	11.563%	$273.0951	$273.10	$273.10	$273.10
Purchase #6	$48.52	12.490%	$54.5801	$54.58	$54.60	$54.60
Purchase #7	$229.85	4.631%	$240.4944	$240.49	$240.50	$240.50
7 purchase totals =	$1,122.88		$1,228.4588	$1,228.46	$1,228.50	$1,228.50