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	$129.29	9.429%	$141.4808	$141.48	$141.50	$141.50
Purchase #2	$47.72	8.834%	$51.9356	$51.94	$51.95	$51.90
Purchase #3	$115.38	5.392%	$121.6013	$121.60	$121.60	$121.60
Purchase #4	$145.87	13.520%	$165.5916	$165.59	$165.60	$165.60
Purchase #5	$117.45	8.463%	$127.3898	$127.39	$127.40	$127.40
Purchase #6	$98.32	6.620%	$104.8288	$104.83	$104.85	$104.80
Purchase #7	$71.73	9.402%	$78.4741	$78.47	$78.45	$78.50
7 purchase totals =	$725.76		$791.3020	$791.30	$791.35	$791.30