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	$208.39	12.411%	$234.2533	$234.25	$234.25	$234.30
Purchase #2	$181.48	6.430%	$193.1492	$193.15	$193.15	$193.10
Purchase #3	$225.53	12.207%	$253.0604	$253.06	$253.05	$253.10
Purchase #4	$38.79	9.148%	$42.3385	$42.34	$42.35	$42.30
Purchase #5	$200.57	6.830%	$214.2689	$214.27	$214.25	$214.30
Purchase #6	$83.28	8.768%	$90.582	$90.58	$90.60	$90.60
Purchase #7	$184.96	13.796%	$210.4771	$210.48	$210.50	$210.50
7 purchase totals =	$1,123.00		$1,238.1294	$1,238.13	$1,238.15	$1,238.20