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	$155.37	10.638%	$171.8983	$171.90	$171.90	$171.90
Purchase #2	$98.55	9.739%	$108.1478	$108.15	$108.15	$108.10
Purchase #3	$104.52	4.331%	$109.0468	$109.05	$109.05	$109.00
Purchase #4	$238.29	12.237%	$267.4495	$267.45	$267.45	$267.40
Purchase #5	$101.88	10.779%	$112.8616	$112.86	$112.85	$112.90
Purchase #6	$137.39	5.473%	$144.9094	$144.91	$144.90	$144.90
Purchase #7	$247.70	8.472%	$268.6851	$268.69	$268.70	$268.70
7 purchase totals =	$1,083.70		$1,182.9985	$1,183.01	$1,183.00	$1,182.90