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	$67.70	11.227%	$75.3007	$75.30	$75.30	$75.30
Purchase #2	$130.45	6.693%	$139.181	$139.18	$139.20	$139.20
Purchase #3	$188.59	13.119%	$213.3311	$213.33	$213.35	$213.30
Purchase #4	$116.52	12.275%	$130.8228	$130.82	$130.80	$130.80
Purchase #5	$95.42	5.704%	$100.8628	$100.86	$100.85	$100.90
Purchase #6	$246.36	6.201%	$261.6368	$261.64	$261.65	$261.60
Purchase #7	$20.32	7.402%	$21.8241	$21.82	$21.80	$21.80
7 purchase totals =	$865.36		$942.9593	$942.95	$942.95	$942.90