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	$226.84	9.544%	$248.4896	$248.49	$248.50	$248.50
Purchase #2	$247.96	10.159%	$273.1503	$273.15	$273.15	$273.20
Purchase #3	$91.46	3.304%	$94.4818	$94.48	$94.50	$94.50
Purchase #4	$85.83	3.843%	$89.1284	$89.13	$89.15	$89.10
Purchase #5	$235.37	10.693%	$260.5381	$260.54	$260.55	$260.50
Purchase #6	$119.86	3.572%	$124.1414	$124.14	$124.15	$124.10
Purchase #7	$86.37	5.102%	$90.7766	$90.78	$90.80	$90.80
7 purchase totals =	$1,093.69		$1,180.7062	$1,180.71	$1,180.80	$1,180.70