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	$25.52	7.119%	$27.3368	$27.34	$27.35	$27.30
Purchase #2	$53.75	11.492%	$59.927	$59.93	$59.95	$59.90
Purchase #3	$94.53	5.125%	$99.3747	$99.37	$99.35	$99.40
Purchase #4	$241.75	9.516%	$264.7549	$264.75	$264.75	$264.80
Purchase #5	$90.64	9.366%	$99.1293	$99.13	$99.15	$99.10
Purchase #6	$125.38	9.434%	$137.2083	$137.21	$137.20	$137.20
Purchase #7	$123.54	8.758%	$134.3596	$134.36	$134.35	$134.40
7 purchase totals =	$755.11		$822.0906	$822.09	$822.10	$822.10