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	$79.75	13.212%	$90.2866	$90.29	$90.30	$90.30
Purchase #2	$169.78	10.293%	$187.2555	$187.26	$187.25	$187.30
Purchase #3	$241.45	4.183%	$251.5499	$251.55	$251.55	$251.50
Purchase #4	$43.25	11.427%	$48.1922	$48.19	$48.20	$48.20
Purchase #5	$110.38	12.765%	$124.47	$124.47	$124.45	$124.50
Purchase #6	$239.98	11.577%	$267.7625	$267.76	$267.75	$267.80
Purchase #7	$90.56	11.317%	$100.8087	$100.81	$100.80	$100.80
7 purchase totals =	$975.15		$1,070.3254	$1,070.33	$1,070.30	$1,070.40