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	$156.36	7.644%	$168.3122	$168.31	$168.30	$168.30
Purchase #2	$144.96	8.212%	$156.8641	$156.86	$156.85	$156.90
Purchase #3	$72.65	6.132%	$77.1049	$77.10	$77.10	$77.10
Purchase #4	$89.54	8.162%	$96.8483	$96.85	$96.85	$96.80
Purchase #5	$14.30	5.771%	$15.1253	$15.13	$15.15	$15.10
Purchase #6	$87.79	12.161%	$98.4661	$98.47	$98.45	$98.50
Purchase #7	$10.58	3.317%	$10.9309	$10.93	$10.95	$10.90
7 purchase totals =	$576.18		$623.6518	$623.65	$623.65	$623.60