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	$20.53	10.299%	$22.6444	$22.64	$22.65	$22.60
Purchase #2	$183.35	10.646%	$202.8694	$202.87	$202.85	$202.90
Purchase #3	$169.78	5.112%	$178.4592	$178.46	$178.45	$178.50
Purchase #4	$250.50	13.373%	$283.9994	$284.00	$284.00	$284.00
Purchase #5	$152.88	12.533%	$172.0405	$172.04	$172.05	$172.00
Purchase #6	$85.65	4.585%	$89.5771	$89.58	$89.60	$89.60
Purchase #7	$68.90	3.495%	$71.3081	$71.31	$71.30	$71.30
7 purchase totals =	$931.59		$1,020.8981	$1,020.90	$1,020.90	$1,020.90