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	$179.80	11.523%	$200.5184	$200.52	$200.50	$200.50
Purchase #2	$47.77	6.803%	$51.0198	$51.02	$51.00	$51.00
Purchase #3	$219.73	9.304%	$240.1737	$240.17	$240.15	$240.20
Purchase #4	$39.54	9.116%	$43.1445	$43.14	$43.15	$43.10
Purchase #5	$92.64	8.346%	$100.3717	$100.37	$100.35	$100.40
Purchase #6	$36.86	13.860%	$41.9688	$41.97	$41.95	$42.00
Purchase #7	$147.39	11.770%	$164.7378	$164.74	$164.75	$164.70
7 purchase totals =	$763.73		$841.9347	$841.93	$841.85	$841.90