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	$14.72	7.156%	$15.7734	$15.77	$15.75	$15.80
Purchase #2	$219.64	4.496%	$229.515	$229.52	$229.50	$229.50
Purchase #3	$186.59	3.749%	$193.5853	$193.59	$193.60	$193.60
Purchase #4	$149.66	7.219%	$160.464	$160.46	$160.45	$160.50
Purchase #5	$131.76	13.846%	$150.0035	$150.00	$150.00	$150.00
Purchase #6	$99.87	13.780%	$113.6321	$113.63	$113.65	$113.60
Purchase #7	$24.71	12.777%	$27.8672	$27.87	$27.85	$27.90
7 purchase totals =	$826.95		$890.8405	$890.84	$890.80	$890.90