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	$7.58	9.853%	$8.3269	$8.33	$8.35	$8.30
Purchase #2	$192.79	4.213%	$200.9122	$200.91	$200.90	$200.90
Purchase #3	$29.72	12.471%	$33.4264	$33.43	$33.45	$33.40
Purchase #4	$104.72	4.268%	$109.1894	$109.19	$109.20	$109.20
Purchase #5	$139.65	12.169%	$156.644	$156.64	$156.65	$156.60
Purchase #6	$213.66	13.376%	$242.2392	$242.24	$242.25	$242.20
Purchase #7	$128.75	10.410%	$142.1529	$142.15	$142.15	$142.20
7 purchase totals =	$816.87		$892.8910	$892.89	$892.95	$892.80