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	$75.83	6.777%	$80.969	$80.97	$80.95	$81.00
Purchase #2	$25.82	12.756%	$29.1136	$29.11	$29.10	$29.10
Purchase #3	$63.99	13.808%	$72.8257	$72.83	$72.85	$72.80
Purchase #4	$30.44	5.146%	$32.0064	$32.01	$32.00	$32.00
Purchase #5	$37.40	8.753%	$40.6736	$40.67	$40.65	$40.70
Purchase #6	$36.93	3.827%	$38.3433	$38.34	$38.35	$38.30
Purchase #7	$79.72	13.219%	$90.2582	$90.26	$90.25	$90.30
7 purchase totals =	$350.13		$384.1898	$384.19	$384.15	$384.20