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	$23.64	11.775%	$26.4236	$26.42	$26.40	$26.40
Purchase #2	$95.89	10.334%	$105.7993	$105.80	$105.80	$105.80
Purchase #3	$145.71	7.450%	$156.5654	$156.57	$156.55	$156.60
Purchase #4	$79.68	3.214%	$82.2409	$82.24	$82.25	$82.20
Purchase #5	$22.90	7.270%	$24.5648	$24.56	$24.55	$24.60
Purchase #6	$87.38	3.218%	$90.1919	$90.19	$90.20	$90.20
Purchase #7	$145.32	3.556%	$150.4876	$150.49	$150.50	$150.50
7 purchase totals =	$600.52		$636.2735	$636.27	$636.25	$636.30