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	$239.30	7.704%	$257.7357	$257.74	$257.75	$257.70
Purchase #2	$64.63	12.199%	$72.5142	$72.51	$72.50	$72.50
Purchase #3	$71.71	9.261%	$78.3511	$78.35	$78.35	$78.40
Purchase #4	$128.98	7.473%	$138.6187	$138.62	$138.60	$138.60
Purchase #5	$85.52	3.229%	$88.2814	$88.28	$88.30	$88.30
Purchase #6	$202.49	12.801%	$228.4107	$228.41	$228.40	$228.40
Purchase #7	$17.60	5.319%	$18.5361	$18.54	$18.55	$18.50
7 purchase totals =	$810.23		$882.4479	$882.45	$882.45	$882.40