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	$83.47	8.221%	$90.3321	$90.33	$90.35	$90.30
Purchase #2	$246.83	4.611%	$258.2113	$258.21	$258.20	$258.20
Purchase #3	$147.80	9.465%	$161.7893	$161.79	$161.80	$161.80
Purchase #4	$34.93	4.825%	$36.6154	$36.62	$36.60	$36.60
Purchase #5	$38.92	7.797%	$41.9546	$41.95	$41.95	$42.00
Purchase #6	$118.98	3.642%	$123.3133	$123.31	$123.30	$123.30
Purchase #7	$85.89	3.850%	$89.1968	$89.20	$89.20	$89.20
7 purchase totals =	$756.82		$801.4128	$801.41	$801.40	$801.40