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	$181.38	4.382%	$189.3281	$189.33	$189.35	$189.30
Purchase #2	$21.41	13.115%	$24.2179	$24.22	$24.20	$24.20
Purchase #3	$28.32	9.756%	$31.0829	$31.08	$31.10	$31.10
Purchase #4	$62.42	7.557%	$67.1371	$67.14	$67.15	$67.10
Purchase #5	$161.47	3.105%	$166.4836	$166.48	$166.50	$166.50
Purchase #6	$83.91	10.696%	$92.885	$92.89	$92.90	$92.90
Purchase #7	$113.55	13.849%	$129.2755	$129.28	$129.30	$129.30
7 purchase totals =	$652.46		$700.4101	$700.42	$700.50	$700.40