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	$21.97	6.649%	$23.4308	$23.43	$23.45	$23.40
Purchase #2	$56.49	5.441%	$59.5636	$59.56	$59.55	$59.60
Purchase #3	$228.61	9.760%	$250.9223	$250.92	$250.90	$250.90
Purchase #4	$201.78	4.858%	$211.5825	$211.58	$211.60	$211.60
Purchase #5	$244.64	4.480%	$255.5999	$255.60	$255.60	$255.60
Purchase #6	$84.76	12.197%	$95.0982	$95.10	$95.10	$95.10
Purchase #7	$171.73	6.665%	$183.1758	$183.18	$183.20	$183.20
7 purchase totals =	$1,009.98		$1,079.3731	$1,079.37	$1,079.40	$1,079.40