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	$134.65	6.534%	$143.448	$143.45	$143.45	$143.40
Purchase #2	$82.47	9.158%	$90.0226	$90.02	$90.00	$90.00
Purchase #3	$136.72	7.138%	$146.4791	$146.48	$146.50	$146.50
Purchase #4	$186.59	7.689%	$200.9369	$200.94	$200.95	$200.90
Purchase #5	$154.59	13.454%	$175.3885	$175.39	$175.40	$175.40
Purchase #6	$7.61	10.254%	$8.3903	$8.39	$8.40	$8.40
Purchase #7	$136.31	8.256%	$147.5638	$147.56	$147.55	$147.60
7 purchase totals =	$838.94		$912.2292	$912.23	$912.25	$912.20