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	$236.94	13.549%	$269.043	$269.04	$269.05	$269.00
Purchase #2	$233.51	6.276%	$248.1651	$248.17	$248.15	$248.20
Purchase #3	$23.82	11.279%	$26.5067	$26.51	$26.50	$26.50
Purchase #4	$135.93	6.543%	$144.8239	$144.82	$144.80	$144.80
Purchase #5	$131.91	3.470%	$136.4873	$136.49	$136.50	$136.50
Purchase #6	$85.80	5.821%	$90.7944	$90.79	$90.80	$90.80
Purchase #7	$158.70	3.691%	$164.5576	$164.56	$164.55	$164.60
7 purchase totals =	$1,006.61		$1,080.3780	$1,080.38	$1,080.35	$1,080.40