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	$40.69	6.155%	$43.1945	$43.19	$43.20	$43.20
Purchase #2	$148.96	12.697%	$167.8735	$167.87	$167.85	$167.90
Purchase #3	$190.52	11.430%	$212.2964	$212.30	$212.30	$212.30
Purchase #4	$14.63	6.475%	$15.5773	$15.58	$15.60	$15.60
Purchase #5	$77.27	10.626%	$85.4807	$85.48	$85.50	$85.50
Purchase #6	$21.57	11.175%	$23.9804	$23.98	$24.00	$24.00
Purchase #7	$131.69	6.244%	$139.9127	$139.91	$139.90	$139.90
7 purchase totals =	$625.33		$688.3155	$688.31	$688.35	$688.40