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	$18.30	9.782%	$20.0901	$20.09	$20.10	$20.10
Purchase #2	$67.39	6.438%	$71.7286	$71.73	$71.75	$71.70
Purchase #3	$110.51	9.397%	$120.8946	$120.89	$120.90	$120.90
Purchase #4	$240.66	11.586%	$268.5429	$268.54	$268.55	$268.50
Purchase #5	$81.32	9.660%	$89.1755	$89.18	$89.20	$89.20
Purchase #6	$172.31	8.866%	$187.587	$187.59	$187.60	$187.60
Purchase #7	$113.37	9.680%	$124.3442	$124.34	$124.35	$124.30
7 purchase totals =	$803.86		$882.3629	$882.36	$882.45	$882.30