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	$148.76	13.534%	$168.8932	$168.89	$168.90	$168.90
Purchase #2	$117.89	5.667%	$124.5708	$124.57	$124.55	$124.60
Purchase #3	$63.28	13.568%	$71.8658	$71.87	$71.85	$71.90
Purchase #4	$82.25	11.220%	$91.4785	$91.48	$91.50	$91.50
Purchase #5	$232.62	6.731%	$248.2777	$248.28	$248.30	$248.30
Purchase #6	$61.26	13.521%	$69.543	$69.54	$69.55	$69.50
Purchase #7	$100.41	4.725%	$105.1544	$105.15	$105.15	$105.20
7 purchase totals =	$806.47		$879.7834	$879.78	$879.80	$879.90