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	$219.82	13.486%	$249.4649	$249.46	$249.45	$249.50
Purchase #2	$72.96	7.797%	$78.6487	$78.65	$78.65	$78.60
Purchase #3	$147.92	7.866%	$159.5554	$159.56	$159.55	$159.60
Purchase #4	$38.42	4.533%	$40.1616	$40.16	$40.15	$40.20
Purchase #5	$211.91	3.686%	$219.721	$219.72	$219.70	$219.70
Purchase #6	$59.88	12.438%	$67.3279	$67.33	$67.35	$67.30
Purchase #7	$42.74	9.675%	$46.8751	$46.88	$46.90	$46.90
7 purchase totals =	$793.65		$861.7546	$861.76	$861.75	$861.80