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	$123.86	12.301%	$139.096	$139.10	$139.10	$139.10
Purchase #2	$169.50	13.666%	$192.6639	$192.66	$192.65	$192.70
Purchase #3	$89.90	5.348%	$94.7079	$94.71	$94.70	$94.70
Purchase #4	$162.67	3.802%	$168.8547	$168.85	$168.85	$168.90
Purchase #5	$69.27	13.798%	$78.8279	$78.83	$78.85	$78.80
Purchase #6	$81.61	13.630%	$92.7334	$92.73	$92.75	$92.70
Purchase #7	$193.67	5.163%	$203.6692	$203.67	$203.65	$203.70
7 purchase totals =	$890.48		$970.5530	$970.55	$970.55	$970.60