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	$141.41	3.696%	$146.6365	$146.64	$146.65	$146.60
Purchase #2	$34.99	5.852%	$37.0376	$37.04	$37.05	$37.00
Purchase #3	$247.97	8.864%	$269.9501	$269.95	$269.95	$270.00
Purchase #4	$189.68	3.559%	$196.4307	$196.43	$196.45	$196.40
Purchase #5	$112.86	13.838%	$128.4776	$128.48	$128.50	$128.50
Purchase #6	$229.47	5.267%	$241.5562	$241.56	$241.55	$241.60
Purchase #7	$232.50	6.818%	$248.3519	$248.35	$248.35	$248.40
7 purchase totals =	$1,188.88		$1,268.4406	$1,268.45	$1,268.50	$1,268.50