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	$79.86	9.345%	$87.3229	$87.32	$87.30	$87.30
Purchase #2	$200.82	12.747%	$226.4185	$226.42	$226.40	$226.40
Purchase #3	$90.72	11.228%	$100.906	$100.91	$100.90	$100.90
Purchase #4	$60.60	6.479%	$64.5263	$64.53	$64.55	$64.50
Purchase #5	$25.57	8.827%	$27.8271	$27.83	$27.85	$27.80
Purchase #6	$120.70	9.762%	$132.4827	$132.48	$132.50	$132.50
Purchase #7	$82.93	7.765%	$89.3695	$89.37	$89.35	$89.40
7 purchase totals =	$661.20		$728.8530	$728.86	$728.85	$728.80