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	$75.82	12.623%	$85.3908	$85.39	$85.40	$85.40
Purchase #2	$17.63	4.195%	$18.3696	$18.37	$18.35	$18.40
Purchase #3	$39.59	7.175%	$42.4306	$42.43	$42.45	$42.40
Purchase #4	$183.63	8.325%	$198.9172	$198.92	$198.90	$198.90
Purchase #5	$24.44	4.486%	$25.5364	$25.54	$25.55	$25.50
Purchase #6	$58.25	10.378%	$64.2952	$64.30	$64.30	$64.30
Purchase #7	$96.72	7.478%	$103.9527	$103.95	$103.95	$104.00
7 purchase totals =	$496.08		$538.8925	$538.90	$538.90	$538.90