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	$79.56	6.232%	$84.5182	$84.52	$84.50	$84.50
Purchase #2	$172.68	13.834%	$196.5686	$196.57	$196.55	$196.60
Purchase #3	$156.33	13.193%	$176.9546	$176.95	$176.95	$177.00
Purchase #4	$225.37	6.470%	$239.9514	$239.95	$239.95	$240.00
Purchase #5	$85.61	5.394%	$90.2278	$90.23	$90.25	$90.20
Purchase #6	$248.58	3.369%	$256.9547	$256.95	$256.95	$257.00
Purchase #7	$184.82	13.215%	$209.244	$209.24	$209.25	$209.20
7 purchase totals =	$1,152.95		$1,254.4193	$1,254.41	$1,254.40	$1,254.50