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	$148.61	10.640%	$164.4221	$164.42	$164.40	$164.40
Purchase #2	$37.72	9.833%	$41.429	$41.43	$41.45	$41.40
Purchase #3	$147.25	13.607%	$167.2863	$167.29	$167.30	$167.30
Purchase #4	$162.49	5.144%	$170.8485	$170.85	$170.85	$170.80
Purchase #5	$99.96	9.759%	$109.7151	$109.72	$109.70	$109.70
Purchase #6	$74.83	4.713%	$78.3567	$78.36	$78.35	$78.40
Purchase #7	$177.32	4.525%	$185.3437	$185.34	$185.35	$185.30
7 purchase totals =	$848.18		$917.4014	$917.41	$917.40	$917.30