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	$92.73	7.354%	$99.5494	$99.55	$99.55	$99.50
Purchase #2	$104.47	10.279%	$115.2085	$115.21	$115.20	$115.20
Purchase #3	$33.25	12.778%	$37.4987	$37.50	$37.50	$37.50
Purchase #4	$88.47	4.622%	$92.5591	$92.56	$92.55	$92.60
Purchase #5	$245.65	5.324%	$258.7284	$258.73	$258.75	$258.70
Purchase #6	$128.62	12.628%	$144.8621	$144.86	$144.85	$144.90
Purchase #7	$52.84	6.700%	$56.3803	$56.38	$56.40	$56.40
7 purchase totals =	$746.03		$804.7865	$804.79	$804.80	$804.80