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	$51.38	5.131%	$54.0163	$54.02	$54.00	$54.00
Purchase #2	$214.61	7.840%	$231.4354	$231.44	$231.45	$231.40
Purchase #3	$80.66	3.282%	$83.3073	$83.31	$83.30	$83.30
Purchase #4	$139.50	3.715%	$144.6824	$144.68	$144.70	$144.70
Purchase #5	$196.29	11.382%	$218.6317	$218.63	$218.65	$218.60
Purchase #6	$79.70	11.684%	$89.0121	$89.01	$89.00	$89.00
Purchase #7	$139.69	12.592%	$157.2798	$157.28	$157.30	$157.30
7 purchase totals =	$901.83		$978.3650	$978.37	$978.40	$978.30