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	$74.34	5.680%	$78.5625	$78.56	$78.55	$78.60
Purchase #2	$156.84	13.134%	$177.4394	$177.44	$177.45	$177.40
Purchase #3	$205.72	7.803%	$221.7723	$221.77	$221.75	$221.80
Purchase #4	$73.41	12.168%	$82.3425	$82.34	$82.35	$82.30
Purchase #5	$90.97	5.401%	$95.8833	$95.88	$95.90	$95.90
Purchase #6	$126.83	6.387%	$134.9306	$134.93	$134.95	$134.90
Purchase #7	$115.56	10.313%	$127.4777	$127.48	$127.50	$127.50
7 purchase totals =	$843.67		$918.4083	$918.40	$918.45	$918.40