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	$150.97	5.820%	$159.7565	$159.76	$159.75	$159.80
Purchase #2	$98.66	11.363%	$109.8707	$109.87	$109.85	$109.90
Purchase #3	$237.29	5.363%	$250.0159	$250.02	$250.00	$250.00
Purchase #4	$17.36	12.348%	$19.5036	$19.50	$19.50	$19.50
Purchase #5	$122.85	13.152%	$139.0072	$139.01	$139.00	$139.00
Purchase #6	$76.80	13.141%	$86.8923	$86.89	$86.90	$86.90
Purchase #7	$188.55	11.572%	$210.369	$210.37	$210.35	$210.40
7 purchase totals =	$892.48		$975.4152	$975.42	$975.35	$975.50