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	$152.58	12.247%	$171.2665	$171.27	$171.25	$171.30
Purchase #2	$225.37	10.423%	$248.8603	$248.86	$248.85	$248.90
Purchase #3	$85.56	11.422%	$95.3327	$95.33	$95.35	$95.30
Purchase #4	$245.95	8.725%	$267.4091	$267.41	$267.40	$267.40
Purchase #5	$41.90	13.642%	$47.616	$47.62	$47.60	$47.60
Purchase #6	$97.91	7.498%	$105.2513	$105.25	$105.25	$105.30
Purchase #7	$162.83	5.680%	$172.0787	$172.08	$172.10	$172.10
7 purchase totals =	$1,012.10		$1,107.8146	$1,107.82	$1,107.80	$1,107.90