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	$140.42	10.724%	$155.4786	$155.48	$155.50	$155.50
Purchase #2	$88.75	4.375%	$92.6328	$92.63	$92.65	$92.60
Purchase #3	$179.55	11.371%	$199.9666	$199.97	$199.95	$200.00
Purchase #4	$40.90	3.266%	$42.2358	$42.24	$42.25	$42.20
Purchase #5	$19.43	6.733%	$20.7382	$20.74	$20.75	$20.70
Purchase #6	$63.40	4.109%	$66.0051	$66.01	$66.00	$66.00
Purchase #7	$140.75	7.843%	$151.789	$151.79	$151.80	$151.80
7 purchase totals =	$673.20		$728.8461	$728.86	$728.90	$728.80