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	$130.55	9.786%	$143.3256	$143.33	$143.35	$143.30
Purchase #2	$139.45	8.864%	$151.8108	$151.81	$151.80	$151.80
Purchase #3	$88.79	13.599%	$100.8646	$100.86	$100.85	$100.90
Purchase #4	$76.47	8.185%	$82.7291	$82.73	$82.75	$82.70
Purchase #5	$196.70	12.809%	$221.8953	$221.90	$221.90	$221.90
Purchase #6	$41.81	10.522%	$46.2092	$46.21	$46.20	$46.20
Purchase #7	$81.93	6.438%	$87.2047	$87.20	$87.20	$87.20
7 purchase totals =	$755.70		$834.0393	$834.04	$834.05	$834.00