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	$156.45	3.723%	$162.2746	$162.27	$162.25	$162.30
Purchase #2	$39.27	7.194%	$42.0951	$42.10	$42.10	$42.10
Purchase #3	$206.26	5.867%	$218.3613	$218.36	$218.35	$218.40
Purchase #4	$79.88	13.378%	$90.5663	$90.57	$90.55	$90.60
Purchase #5	$206.96	12.661%	$233.1632	$233.16	$233.15	$233.20
Purchase #6	$162.27	10.311%	$179.0017	$179.00	$179.00	$179.00
Purchase #7	$41.51	8.665%	$45.1068	$45.11	$45.10	$45.10
7 purchase totals =	$892.60		$970.5690	$970.57	$970.50	$970.70