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	$6.76	13.743%	$7.689	$7.69	$7.70	$7.70
Purchase #2	$85.70	9.858%	$94.1483	$94.15	$94.15	$94.10
Purchase #3	$57.56	3.434%	$59.5366	$59.54	$59.55	$59.50
Purchase #4	$84.81	4.230%	$88.3975	$88.40	$88.40	$88.40
Purchase #5	$58.88	13.371%	$66.7528	$66.75	$66.75	$66.80
Purchase #6	$228.86	9.434%	$250.4507	$250.45	$250.45	$250.50
Purchase #7	$212.59	4.866%	$222.9346	$222.93	$222.95	$222.90
7 purchase totals =	$735.16		$789.9095	$789.91	$789.95	$789.90