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	$39.43	3.154%	$40.6736	$40.67	$40.65	$40.70
Purchase #2	$85.34	12.219%	$95.7677	$95.77	$95.75	$95.80
Purchase #3	$58.49	10.503%	$64.6332	$64.63	$64.65	$64.60
Purchase #4	$57.64	13.432%	$65.3822	$65.38	$65.40	$65.40
Purchase #5	$51.82	5.832%	$54.8421	$54.84	$54.85	$54.80
Purchase #6	$232.31	10.242%	$256.1032	$256.10	$256.10	$256.10
Purchase #7	$80.40	12.599%	$90.5296	$90.53	$90.55	$90.50
7 purchase totals =	$605.43		$667.9316	$667.92	$667.95	$667.90