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	$42.74	5.531%	$45.1039	$45.10	$45.10	$45.10
Purchase #2	$59.78	10.822%	$66.2494	$66.25	$66.25	$66.20
Purchase #3	$55.58	13.104%	$62.8632	$62.86	$62.85	$62.90
Purchase #4	$209.52	3.361%	$216.562	$216.56	$216.55	$216.60
Purchase #5	$195.38	8.377%	$211.747	$211.75	$211.75	$211.70
Purchase #6	$70.25	12.198%	$78.8191	$78.82	$78.80	$78.80
Purchase #7	$144.74	7.216%	$155.1844	$155.18	$155.20	$155.20
7 purchase totals =	$777.99		$836.5290	$836.52	$836.50	$836.50