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	$123.98	3.448%	$128.2548	$128.25	$128.25	$128.30
Purchase #2	$199.90	4.183%	$208.2618	$208.26	$208.25	$208.30
Purchase #3	$42.46	10.220%	$46.7994	$46.80	$46.80	$46.80
Purchase #4	$70.73	8.218%	$76.5426	$76.54	$76.55	$76.50
Purchase #5	$144.50	4.378%	$150.8262	$150.83	$150.85	$150.80
Purchase #6	$75.42	10.800%	$83.5654	$83.57	$83.55	$83.60
Purchase #7	$146.65	12.448%	$164.905	$164.91	$164.90	$164.90
7 purchase totals =	$803.64		$859.1552	$859.16	$859.15	$859.20