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	$37.32	4.176%	$38.8785	$38.88	$38.90	$38.90
Purchase #2	$146.87	13.213%	$166.2759	$166.28	$166.30	$166.30
Purchase #3	$137.96	13.584%	$156.7005	$156.70	$156.70	$156.70
Purchase #4	$83.38	6.547%	$88.8389	$88.84	$88.85	$88.80
Purchase #5	$145.80	12.725%	$164.3531	$164.35	$164.35	$164.40
Purchase #6	$203.73	12.377%	$228.9457	$228.95	$228.95	$228.90
Purchase #7	$53.69	13.381%	$60.8743	$60.87	$60.85	$60.90
7 purchase totals =	$808.75		$904.8669	$904.87	$904.90	$904.90