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	$215.75	13.255%	$244.3477	$244.35	$244.35	$244.30
Purchase #2	$250.70	11.505%	$279.543	$279.54	$279.55	$279.50
Purchase #3	$226.58	7.254%	$243.0161	$243.02	$243.00	$243.00
Purchase #4	$182.35	9.541%	$199.748	$199.75	$199.75	$199.70
Purchase #5	$152.33	10.825%	$168.8197	$168.82	$168.80	$168.80
Purchase #6	$119.56	10.243%	$131.8065	$131.81	$131.80	$131.80
Purchase #7	$29.97	11.542%	$33.4291	$33.43	$33.45	$33.40
7 purchase totals =	$1,177.24		$1,300.7101	$1,300.72	$1,300.70	$1,300.50