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	$104.98	4.179%	$109.3671	$109.37	$109.35	$109.40
Purchase #2	$37.98	10.643%	$42.0222	$42.02	$42.00	$42.00
Purchase #3	$137.86	10.737%	$152.662	$152.66	$152.65	$152.70
Purchase #4	$9.37	7.278%	$10.0519	$10.05	$10.05	$10.10
Purchase #5	$160.88	12.447%	$180.9047	$180.90	$180.90	$180.90
Purchase #6	$148.75	10.369%	$164.1739	$164.17	$164.15	$164.20
Purchase #7	$117.25	12.600%	$132.0235	$132.02	$132.00	$132.00
7 purchase totals =	$717.07		$791.2053	$791.19	$791.10	$791.30