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	$109.93	12.650%	$123.8361	$123.84	$123.85	$123.80
Purchase #2	$160.84	13.483%	$182.5261	$182.53	$182.55	$182.50
Purchase #3	$37.66	13.248%	$42.6492	$42.65	$42.65	$42.60
Purchase #4	$55.79	10.596%	$61.7015	$61.70	$61.70	$61.70
Purchase #5	$41.25	4.258%	$43.0064	$43.01	$43.00	$43.00
Purchase #6	$165.38	13.653%	$187.9593	$187.96	$187.95	$188.00
Purchase #7	$65.49	13.392%	$74.2604	$74.26	$74.25	$74.30
7 purchase totals =	$636.34		$715.9390	$715.95	$715.95	$715.90