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	$187.90	6.672%	$200.4367	$200.44	$200.45	$200.40
Purchase #2	$38.56	13.702%	$43.8435	$43.84	$43.85	$43.80
Purchase #3	$86.34	9.505%	$94.5466	$94.55	$94.55	$94.50
Purchase #4	$182.25	4.694%	$190.8048	$190.80	$190.80	$190.80
Purchase #5	$136.35	5.709%	$144.1342	$144.13	$144.15	$144.10
Purchase #6	$43.81	11.441%	$48.8223	$48.82	$48.80	$48.80
Purchase #7	$161.99	8.217%	$175.3007	$175.30	$175.30	$175.30
7 purchase totals =	$837.20		$897.8888	$897.88	$897.90	$897.70