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	$138.83	3.635%	$143.8765	$143.88	$143.90	$143.90
Purchase #2	$206.85	11.108%	$229.8269	$229.83	$229.85	$229.80
Purchase #3	$79.41	3.492%	$82.183	$82.18	$82.20	$82.20
Purchase #4	$94.76	4.449%	$98.9759	$98.98	$99.00	$99.00
Purchase #5	$138.98	12.651%	$156.5624	$156.56	$156.55	$156.60
Purchase #6	$125.65	5.707%	$132.8208	$132.82	$132.80	$132.80
Purchase #7	$53.47	6.860%	$57.138	$57.14	$57.15	$57.10
7 purchase totals =	$837.95		$901.3835	$901.39	$901.45	$901.40