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	$41.41	3.771%	$42.9716	$42.97	$42.95	$43.00
Purchase #2	$170.90	8.570%	$185.5461	$185.55	$185.55	$185.50
Purchase #3	$30.55	6.405%	$32.5067	$32.51	$32.50	$32.50
Purchase #4	$101.69	10.567%	$112.4356	$112.44	$112.45	$112.40
Purchase #5	$13.34	12.302%	$14.9811	$14.98	$15.00	$15.00
Purchase #6	$137.46	12.739%	$154.971	$154.97	$154.95	$155.00
Purchase #7	$82.72	3.802%	$85.865	$85.87	$85.85	$85.90
7 purchase totals =	$578.07		$629.2771	$629.29	$629.25	$629.30