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	$115.62	13.710%	$131.4715	$131.47	$131.45	$131.50
Purchase #2	$41.96	7.361%	$45.0487	$45.05	$45.05	$45.00
Purchase #3	$30.91	7.346%	$33.1806	$33.18	$33.20	$33.20
Purchase #4	$51.40	7.814%	$55.4164	$55.42	$55.40	$55.40
Purchase #5	$32.97	10.653%	$36.4823	$36.48	$36.50	$36.50
Purchase #6	$164.41	12.548%	$185.0402	$185.04	$185.05	$185.00
Purchase #7	$207.74	12.116%	$232.9098	$232.91	$232.90	$232.90
7 purchase totals =	$645.01		$719.5495	$719.55	$719.55	$719.50