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	$242.42	4.574%	$253.5083	$253.51	$253.50	$253.50
Purchase #2	$84.72	3.348%	$87.5564	$87.56	$87.55	$87.60
Purchase #3	$245.44	10.539%	$271.3069	$271.31	$271.30	$271.30
Purchase #4	$133.57	3.704%	$138.5174	$138.52	$138.50	$138.50
Purchase #5	$82.83	9.863%	$90.9995	$91.00	$91.00	$91.00
Purchase #6	$46.86	13.651%	$53.2569	$53.26	$53.25	$53.30
Purchase #7	$82.43	9.485%	$90.2485	$90.25	$90.25	$90.20
7 purchase totals =	$918.27		$985.3939	$985.41	$985.35	$985.40