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	$14.36	11.141%	$15.9598	$15.96	$15.95	$16.00
Purchase #2	$172.32	9.630%	$188.9144	$188.91	$188.90	$188.90
Purchase #3	$105.47	4.558%	$110.2773	$110.28	$110.30	$110.30
Purchase #4	$118.44	7.452%	$127.2661	$127.27	$127.25	$127.30
Purchase #5	$242.25	11.263%	$269.5346	$269.53	$269.55	$269.50
Purchase #6	$25.51	10.833%	$28.2735	$28.27	$28.25	$28.30
Purchase #7	$67.98	6.244%	$72.2247	$72.22	$72.20	$72.20
7 purchase totals =	$746.33		$812.4504	$812.44	$812.40	$812.50