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	$160.44	11.774%	$179.3302	$179.33	$179.35	$179.30
Purchase #2	$63.60	3.574%	$65.8731	$65.87	$65.85	$65.90
Purchase #3	$63.32	10.569%	$70.0123	$70.01	$70.00	$70.00
Purchase #4	$119.90	13.791%	$136.4354	$136.44	$136.45	$136.40
Purchase #5	$131.61	11.283%	$146.4596	$146.46	$146.45	$146.50
Purchase #6	$188.43	5.242%	$198.3075	$198.31	$198.30	$198.30
Purchase #7	$90.91	8.223%	$98.3855	$98.39	$98.40	$98.40
7 purchase totals =	$818.21		$894.8036	$894.81	$894.80	$894.80