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	$70.83	10.748%	$78.4428	$78.44	$78.45	$78.40
Purchase #2	$233.88	5.165%	$245.9599	$245.96	$245.95	$246.00
Purchase #3	$92.43	12.359%	$103.8534	$103.85	$103.85	$103.90
Purchase #4	$54.73	8.352%	$59.301	$59.30	$59.30	$59.30
Purchase #5	$230.30	13.320%	$260.976	$260.98	$261.00	$261.00
Purchase #6	$16.98	9.104%	$18.5259	$18.53	$18.55	$18.50
Purchase #7	$23.66	11.797%	$26.4512	$26.45	$26.45	$26.50
7 purchase totals =	$722.81		$793.5102	$793.51	$793.55	$793.60