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	$6.87	12.316%	$7.7161	$7.72	$7.70	$7.70
Purchase #2	$169.83	3.203%	$175.2697	$175.27	$175.25	$175.30
Purchase #3	$233.94	3.802%	$242.8344	$242.83	$242.85	$242.80
Purchase #4	$163.29	13.457%	$185.2639	$185.26	$185.25	$185.30
Purchase #5	$86.71	4.540%	$90.6466	$90.65	$90.65	$90.60
Purchase #6	$79.52	11.180%	$88.4103	$88.41	$88.40	$88.40
Purchase #7	$116.82	10.249%	$128.7929	$128.79	$128.80	$128.80
7 purchase totals =	$856.98		$918.9339	$918.93	$918.90	$918.90