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	$108.36	3.510%	$112.1634	$112.16	$112.15	$112.20
Purchase #2	$65.34	7.275%	$70.0935	$70.09	$70.10	$70.10
Purchase #3	$123.83	12.807%	$139.6889	$139.69	$139.70	$139.70
Purchase #4	$152.50	10.587%	$168.6452	$168.65	$168.65	$168.60
Purchase #5	$238.88	10.329%	$263.5539	$263.55	$263.55	$263.60
Purchase #6	$247.27	10.661%	$273.6315	$273.63	$273.65	$273.60
Purchase #7	$249.77	7.739%	$269.0997	$269.10	$269.10	$269.10
7 purchase totals =	$1,185.95		$1,296.8761	$1,296.87	$1,296.90	$1,296.90