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	$37.70	10.845%	$41.7886	$41.79	$41.80	$41.80
Purchase #2	$234.69	8.435%	$254.4861	$254.49	$254.50	$254.50
Purchase #3	$125.57	9.132%	$137.0371	$137.04	$137.05	$137.00
Purchase #4	$79.44	4.307%	$82.8615	$82.86	$82.85	$82.90
Purchase #5	$236.59	13.199%	$267.8175	$267.82	$267.80	$267.80
Purchase #6	$48.27	12.308%	$54.2111	$54.21	$54.20	$54.20
Purchase #7	$48.30	9.168%	$52.7281	$52.73	$52.75	$52.70
7 purchase totals =	$810.56		$890.9300	$890.94	$890.95	$890.90