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	$76.86	7.862%	$82.9027	$82.90	$82.90	$82.90
Purchase #2	$17.91	13.666%	$20.3576	$20.36	$20.35	$20.40
Purchase #3	$232.36	10.437%	$256.6114	$256.61	$256.60	$256.60
Purchase #4	$231.39	10.616%	$255.9544	$255.95	$255.95	$256.00
Purchase #5	$140.39	10.858%	$155.6335	$155.63	$155.65	$155.60
Purchase #6	$89.71	12.370%	$100.8071	$100.81	$100.80	$100.80
Purchase #7	$6.73	13.222%	$7.6198	$7.62	$7.60	$7.60
7 purchase totals =	$795.35		$879.8865	$879.88	$879.85	$879.90