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	$29.61	9.413%	$32.3972	$32.40	$32.40	$32.40
Purchase #2	$132.54	9.224%	$144.7655	$144.77	$144.75	$144.80
Purchase #3	$37.33	8.237%	$40.4049	$40.40	$40.40	$40.40
Purchase #4	$189.52	9.489%	$207.5036	$207.50	$207.50	$207.50
Purchase #5	$224.33	11.141%	$249.3226	$249.32	$249.30	$249.30
Purchase #6	$154.79	6.140%	$164.2941	$164.29	$164.30	$164.30
Purchase #7	$245.58	6.638%	$261.8816	$261.88	$261.90	$261.90
7 purchase totals =	$1,013.70		$1,100.5695	$1,100.56	$1,100.55	$1,100.60