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	$214.85	12.799%	$242.3487	$242.35	$242.35	$242.30
Purchase #2	$82.56	9.402%	$90.3223	$90.32	$90.30	$90.30
Purchase #3	$116.57	10.655%	$128.9905	$128.99	$129.00	$129.00
Purchase #4	$9.77	11.740%	$10.917	$10.92	$10.90	$10.90
Purchase #5	$30.64	6.481%	$32.6258	$32.63	$32.65	$32.60
Purchase #6	$146.78	13.708%	$166.9006	$166.90	$166.90	$166.90
Purchase #7	$250.72	6.405%	$266.7786	$266.78	$266.80	$266.80
7 purchase totals =	$851.89		$938.8835	$938.89	$938.90	$938.80