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	$82.62	8.408%	$89.5667	$89.57	$89.55	$89.60
Purchase #2	$139.46	5.515%	$147.1512	$147.15	$147.15	$147.20
Purchase #3	$19.89	9.796%	$21.8384	$21.84	$21.85	$21.80
Purchase #4	$53.93	12.231%	$60.5262	$60.53	$60.55	$60.50
Purchase #5	$162.26	10.577%	$179.4222	$179.42	$179.40	$179.40
Purchase #6	$79.83	10.392%	$88.1259	$88.13	$88.15	$88.10
Purchase #7	$59.38	7.278%	$63.7017	$63.70	$63.70	$63.70
7 purchase totals =	$597.37		$650.3323	$650.34	$650.35	$650.30