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	$71.36	12.616%	$80.3628	$80.36	$80.35	$80.40
Purchase #2	$7.49	13.384%	$8.4925	$8.49	$8.50	$8.50
Purchase #3	$168.43	3.631%	$174.5457	$174.55	$174.55	$174.50
Purchase #4	$153.64	11.698%	$171.6128	$171.61	$171.60	$171.60
Purchase #5	$153.95	9.420%	$168.4521	$168.45	$168.45	$168.50
Purchase #6	$95.37	3.165%	$98.3885	$98.39	$98.40	$98.40
Purchase #7	$120.89	9.518%	$132.3963	$132.40	$132.40	$132.40
7 purchase totals =	$771.13		$834.2507	$834.25	$834.25	$834.30