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	$59.45	12.249%	$66.732	$66.73	$66.75	$66.70
Purchase #2	$181.47	8.258%	$196.4558	$196.46	$196.45	$196.50
Purchase #3	$97.48	10.424%	$107.6413	$107.64	$107.65	$107.60
Purchase #4	$135.45	9.423%	$148.2135	$148.21	$148.20	$148.20
Purchase #5	$222.59	5.649%	$235.1641	$235.16	$235.15	$235.20
Purchase #6	$158.27	8.482%	$171.6945	$171.69	$171.70	$171.70
Purchase #7	$150.55	10.565%	$166.4556	$166.46	$166.45	$166.50
7 purchase totals =	$1,005.26		$1,092.3568	$1,092.35	$1,092.35	$1,092.40