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	$44.79	3.571%	$46.3895	$46.39	$46.40	$46.40
Purchase #2	$165.83	9.502%	$181.5872	$181.59	$181.60	$181.60
Purchase #3	$95.88	7.661%	$103.2254	$103.23	$103.25	$103.20
Purchase #4	$243.72	9.487%	$266.8417	$266.84	$266.85	$266.80
Purchase #5	$170.91	10.792%	$189.3546	$189.35	$189.35	$189.40
Purchase #6	$215.76	3.182%	$222.6255	$222.63	$222.65	$222.60
Purchase #7	$64.71	11.155%	$71.9284	$71.93	$71.95	$71.90
7 purchase totals =	$1,001.60		$1,081.9523	$1,081.96	$1,082.05	$1,081.90