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	$41.75	11.367%	$46.4957	$46.50	$46.50	$46.50
Purchase #2	$210.36	7.242%	$225.5943	$225.59	$225.60	$225.60
Purchase #3	$199.76	4.731%	$209.2106	$209.21	$209.20	$209.20
Purchase #4	$98.84	10.287%	$109.0077	$109.01	$109.00	$109.00
Purchase #5	$28.83	11.151%	$32.0448	$32.04	$32.05	$32.00
Purchase #6	$125.59	4.487%	$131.2252	$131.23	$131.25	$131.20
Purchase #7	$57.47	11.831%	$64.2693	$64.27	$64.25	$64.30
7 purchase totals =	$762.60		$817.8476	$817.85	$817.85	$817.80