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	$36.45	10.413%	$40.2455	$40.25	$40.25	$40.20
Purchase #2	$147.40	11.447%	$164.2729	$164.27	$164.25	$164.30
Purchase #3	$54.67	9.384%	$59.8002	$59.80	$59.80	$59.80
Purchase #4	$23.91	7.370%	$25.6722	$25.67	$25.65	$25.70
Purchase #5	$241.27	3.674%	$250.1343	$250.13	$250.15	$250.10
Purchase #6	$217.58	13.300%	$246.5181	$246.52	$246.50	$246.50
Purchase #7	$159.98	12.666%	$180.2431	$180.24	$180.25	$180.20
7 purchase totals =	$881.26		$966.8863	$966.88	$966.85	$966.80