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	$234.41	6.148%	$248.8215	$248.82	$248.80	$248.80
Purchase #2	$40.83	5.370%	$43.0226	$43.02	$43.00	$43.00
Purchase #3	$172.38	5.274%	$181.4713	$181.47	$181.45	$181.50
Purchase #4	$38.52	11.359%	$42.8955	$42.90	$42.90	$42.90
Purchase #5	$155.73	9.731%	$170.8841	$170.88	$170.90	$170.90
Purchase #6	$90.93	12.333%	$102.1444	$102.14	$102.15	$102.10
Purchase #7	$108.45	6.299%	$115.2813	$115.28	$115.30	$115.30
7 purchase totals =	$841.25		$904.5207	$904.51	$904.50	$904.50