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	$104.52	8.395%	$113.2945	$113.29	$113.30	$113.30
Purchase #2	$55.67	7.645%	$59.926	$59.93	$59.95	$59.90
Purchase #3	$78.70	9.745%	$86.3693	$86.37	$86.35	$86.40
Purchase #4	$87.27	3.495%	$90.3201	$90.32	$90.30	$90.30
Purchase #5	$237.62	12.300%	$266.8473	$266.85	$266.85	$266.80
Purchase #6	$90.93	6.543%	$96.8795	$96.88	$96.90	$96.90
Purchase #7	$134.96	13.306%	$152.9178	$152.92	$152.90	$152.90
7 purchase totals =	$789.67		$866.5545	$866.56	$866.55	$866.50