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	$37.50	10.146%	$41.3048	$41.30	$41.30	$41.30
Purchase #2	$225.31	7.755%	$242.7828	$242.78	$242.80	$242.80
Purchase #3	$131.83	7.619%	$141.8741	$141.87	$141.85	$141.90
Purchase #4	$128.38	13.837%	$146.1439	$146.14	$146.15	$146.10
Purchase #5	$26.89	12.814%	$30.3357	$30.34	$30.35	$30.30
Purchase #6	$139.80	8.736%	$152.0129	$152.01	$152.00	$152.00
Purchase #7	$143.98	3.203%	$148.5917	$148.59	$148.60	$148.60
7 purchase totals =	$833.69		$903.0459	$903.03	$903.05	$903.00