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	$128.56	3.747%	$133.3771	$133.38	$133.40	$133.40
Purchase #2	$157.93	6.103%	$167.5685	$167.57	$167.55	$167.60
Purchase #3	$19.82	8.215%	$21.4482	$21.45	$21.45	$21.40
Purchase #4	$77.95	5.585%	$82.3035	$82.30	$82.30	$82.30
Purchase #5	$19.60	11.530%	$21.8599	$21.86	$21.85	$21.90
Purchase #6	$77.97	11.421%	$86.875	$86.88	$86.90	$86.90
Purchase #7	$84.54	13.755%	$96.1685	$96.17	$96.15	$96.20
7 purchase totals =	$566.37		$609.6007	$609.61	$609.60	$609.70