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	$63.72	13.676%	$72.4343	$72.43	$72.45	$72.40
Purchase #2	$40.89	5.744%	$43.2387	$43.24	$43.25	$43.20
Purchase #3	$123.31	5.852%	$130.5261	$130.53	$130.55	$130.50
Purchase #4	$45.50	11.633%	$50.793	$50.79	$50.80	$50.80
Purchase #5	$94.82	11.849%	$106.0552	$106.06	$106.05	$106.10
Purchase #6	$19.73	12.768%	$22.2491	$22.25	$22.25	$22.20
Purchase #7	$85.50	5.571%	$90.2632	$90.26	$90.25	$90.30
7 purchase totals =	$473.47		$515.5596	$515.56	$515.60	$515.50