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	$69.28	13.666%	$78.7478	$78.75	$78.75	$78.70
Purchase #2	$56.76	4.692%	$59.4232	$59.42	$59.40	$59.40
Purchase #3	$139.93	9.743%	$153.5634	$153.56	$153.55	$153.60
Purchase #4	$220.94	4.625%	$231.1585	$231.16	$231.15	$231.20
Purchase #5	$83.52	3.811%	$86.7029	$86.70	$86.70	$86.70
Purchase #6	$245.80	9.751%	$269.768	$269.77	$269.75	$269.80
Purchase #7	$105.27	8.785%	$114.518	$114.52	$114.50	$114.50
7 purchase totals =	$921.50		$993.8818	$993.88	$993.80	$993.90