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	$131.65	10.384%	$145.3205	$145.32	$145.30	$145.30
Purchase #2	$48.49	10.874%	$53.7628	$53.76	$53.75	$53.80
Purchase #3	$54.48	9.372%	$59.5859	$59.59	$59.60	$59.60
Purchase #4	$168.38	13.447%	$191.0221	$191.02	$191.00	$191.00
Purchase #5	$14.34	9.426%	$15.6917	$15.69	$15.70	$15.70
Purchase #6	$18.86	4.769%	$19.7594	$19.76	$19.75	$19.80
Purchase #7	$171.56	8.713%	$186.508	$186.51	$186.50	$186.50
7 purchase totals =	$607.76		$671.6504	$671.65	$671.60	$671.70