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	$88.89	13.104%	$100.5381	$100.54	$100.55	$100.50
Purchase #2	$144.55	7.641%	$155.5951	$155.60	$155.60	$155.60
Purchase #3	$193.40	3.485%	$200.14	$200.14	$200.15	$200.10
Purchase #4	$206.82	11.725%	$231.0696	$231.07	$231.05	$231.10
Purchase #5	$236.57	4.367%	$246.901	$246.90	$246.90	$246.90
Purchase #6	$157.53	7.489%	$169.3274	$169.33	$169.35	$169.30
Purchase #7	$82.60	4.606%	$86.4046	$86.40	$86.40	$86.40
7 purchase totals =	$1,110.36		$1,189.9758	$1,189.98	$1,190.00	$1,189.90