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	$86.68	3.585%	$89.7875	$89.79	$89.80	$89.80
Purchase #2	$197.69	10.390%	$218.23	$218.23	$218.25	$218.20
Purchase #3	$79.31	9.544%	$86.8793	$86.88	$86.90	$86.90
Purchase #4	$155.37	6.374%	$165.2733	$165.27	$165.25	$165.30
Purchase #5	$72.70	12.601%	$81.8609	$81.86	$81.85	$81.90
Purchase #6	$97.76	13.226%	$110.6897	$110.69	$110.70	$110.70
Purchase #7	$218.93	4.105%	$227.9171	$227.92	$227.90	$227.90
7 purchase totals =	$908.44		$980.6378	$980.64	$980.65	$980.70