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	$40.54	4.315%	$42.2893	$42.29	$42.30	$42.30
Purchase #2	$31.32	3.291%	$32.3507	$32.35	$32.35	$32.40
Purchase #3	$234.50	9.825%	$257.5396	$257.54	$257.55	$257.50
Purchase #4	$73.96	13.304%	$83.7996	$83.80	$83.80	$83.80
Purchase #5	$47.74	13.688%	$54.2747	$54.27	$54.25	$54.30
Purchase #6	$5.84	12.661%	$6.5794	$6.58	$6.60	$6.60
Purchase #7	$175.26	4.212%	$182.642	$182.64	$182.65	$182.60
7 purchase totals =	$609.16		$659.4753	$659.47	$659.50	$659.50