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	$78.28	13.848%	$89.1202	$89.12	$89.10	$89.10
Purchase #2	$214.95	5.648%	$227.0904	$227.09	$227.10	$227.10
Purchase #3	$24.92	9.766%	$27.3537	$27.35	$27.35	$27.40
Purchase #4	$185.91	12.508%	$209.1636	$209.16	$209.15	$209.20
Purchase #5	$84.77	4.450%	$88.5423	$88.54	$88.55	$88.50
Purchase #6	$76.48	12.703%	$86.1953	$86.20	$86.20	$86.20
Purchase #7	$247.45	10.521%	$273.4842	$273.48	$273.50	$273.50
7 purchase totals =	$912.76		$1,000.9497	$1,000.94	$1,000.95	$1,001.00