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	$136.25	12.245%	$152.9338	$152.93	$152.95	$152.90
Purchase #2	$180.82	5.586%	$190.9206	$190.92	$190.90	$190.90
Purchase #3	$53.96	4.269%	$56.2636	$56.26	$56.25	$56.30
Purchase #4	$35.38	11.761%	$39.541	$39.54	$39.55	$39.50
Purchase #5	$20.46	3.245%	$21.1239	$21.12	$21.10	$21.10
Purchase #6	$20.93	10.527%	$23.1333	$23.13	$23.15	$23.10
Purchase #7	$86.68	6.700%	$92.4876	$92.49	$92.50	$92.50
7 purchase totals =	$534.48		$576.4038	$576.39	$576.40	$576.30