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	$84.81	6.103%	$89.986	$89.99	$90.00	$90.00
Purchase #2	$95.94	11.800%	$107.2609	$107.26	$107.25	$107.30
Purchase #3	$139.47	4.270%	$145.4254	$145.43	$145.45	$145.40
Purchase #4	$218.54	12.257%	$245.3264	$245.33	$245.35	$245.30
Purchase #5	$240.81	11.444%	$268.3683	$268.37	$268.35	$268.40
Purchase #6	$153.62	9.241%	$167.816	$167.82	$167.80	$167.80
Purchase #7	$111.62	10.460%	$123.2955	$123.30	$123.30	$123.30
7 purchase totals =	$1,044.81		$1,147.4785	$1,147.50	$1,147.50	$1,147.50