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	$74.47	5.665%	$78.6887	$78.69	$78.70	$78.70
Purchase #2	$43.90	7.459%	$47.1745	$47.17	$47.15	$47.20
Purchase #3	$37.51	9.367%	$41.0236	$41.02	$41.00	$41.00
Purchase #4	$250.55	12.210%	$281.1422	$281.14	$281.15	$281.10
Purchase #5	$100.58	8.332%	$108.9603	$108.96	$108.95	$109.00
Purchase #6	$124.78	6.857%	$133.3362	$133.34	$133.35	$133.30
Purchase #7	$233.80	7.607%	$251.5852	$251.59	$251.60	$251.60
7 purchase totals =	$865.59		$941.9107	$941.91	$941.90	$941.90