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	$124.29	10.195%	$136.9614	$136.96	$136.95	$137.00
Purchase #2	$148.98	12.831%	$168.0956	$168.10	$168.10	$168.10
Purchase #3	$248.26	4.399%	$259.181	$259.18	$259.20	$259.20
Purchase #4	$113.76	6.454%	$121.1021	$121.10	$121.10	$121.10
Purchase #5	$85.38	4.496%	$89.2187	$89.22	$89.20	$89.20
Purchase #6	$15.51	10.160%	$17.0858	$17.09	$17.10	$17.10
Purchase #7	$123.78	10.540%	$136.8264	$136.83	$136.85	$136.80
7 purchase totals =	$859.96		$928.4710	$928.48	$928.50	$928.50