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	$66.29	6.349%	$70.4988	$70.50	$70.50	$70.50
Purchase #2	$106.67	11.780%	$119.2357	$119.24	$119.25	$119.20
Purchase #3	$41.76	11.837%	$46.7031	$46.70	$46.70	$46.70
Purchase #4	$105.97	3.183%	$109.343	$109.34	$109.35	$109.30
Purchase #5	$227.52	10.461%	$251.3209	$251.32	$251.30	$251.30
Purchase #6	$143.56	3.507%	$148.5946	$148.59	$148.60	$148.60
Purchase #7	$57.72	7.254%	$61.907	$61.91	$61.90	$61.90
7 purchase totals =	$749.49		$807.6031	$807.60	$807.60	$807.50