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	$88.60	12.150%	$99.3649	$99.36	$99.35	$99.40
Purchase #2	$74.69	10.384%	$82.4458	$82.45	$82.45	$82.40
Purchase #3	$69.90	6.754%	$74.621	$74.62	$74.60	$74.60
Purchase #4	$218.61	11.850%	$244.5153	$244.52	$244.50	$244.50
Purchase #5	$61.84	13.197%	$70.001	$70.00	$70.00	$70.00
Purchase #6	$38.72	13.462%	$43.9325	$43.93	$43.95	$43.90
Purchase #7	$217.56	6.387%	$231.4556	$231.46	$231.45	$231.50
7 purchase totals =	$769.92		$846.3361	$846.34	$846.30	$846.30