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	$154.80	6.229%	$164.4425	$164.44	$164.45	$164.40
Purchase #2	$81.43	10.495%	$89.9761	$89.98	$90.00	$90.00
Purchase #3	$249.48	5.265%	$262.6151	$262.62	$262.60	$262.60
Purchase #4	$115.90	3.272%	$119.6922	$119.69	$119.70	$119.70
Purchase #5	$116.34	10.261%	$128.2776	$128.28	$128.30	$128.30
Purchase #6	$131.27	7.820%	$141.5353	$141.54	$141.55	$141.50
Purchase #7	$54.33	6.216%	$57.7072	$57.71	$57.70	$57.70
7 purchase totals =	$903.55		$964.2460	$964.26	$964.30	$964.20