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	$137.80	6.826%	$147.2062	$147.21	$147.20	$147.20
Purchase #2	$54.61	9.701%	$59.9077	$59.91	$59.90	$59.90
Purchase #3	$51.91	10.556%	$57.3896	$57.39	$57.40	$57.40
Purchase #4	$35.83	3.280%	$37.0052	$37.01	$37.00	$37.00
Purchase #5	$140.70	4.136%	$146.5194	$146.52	$146.50	$146.50
Purchase #6	$57.55	13.497%	$65.3175	$65.32	$65.30	$65.30
Purchase #7	$216.65	4.624%	$226.6679	$226.67	$226.65	$226.70
7 purchase totals =	$695.05		$740.0135	$740.03	$739.95	$740.00