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	$123.61	13.765%	$140.6249	$140.62	$140.60	$140.60
Purchase #2	$121.60	10.624%	$134.5188	$134.52	$134.50	$134.50
Purchase #3	$240.96	8.476%	$261.3838	$261.38	$261.40	$261.40
Purchase #4	$19.62	4.357%	$20.4748	$20.47	$20.45	$20.50
Purchase #5	$66.73	10.134%	$73.4924	$73.49	$73.50	$73.50
Purchase #6	$55.95	3.776%	$58.0627	$58.06	$58.05	$58.10
Purchase #7	$69.45	3.419%	$71.8245	$71.82	$71.80	$71.80
7 purchase totals =	$697.92		$760.3819	$760.36	$760.30	$760.40