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	$178.76	5.433%	$188.472	$188.47	$188.45	$188.50
Purchase #2	$191.33	3.697%	$198.4035	$198.40	$198.40	$198.40
Purchase #3	$55.54	6.809%	$59.3217	$59.32	$59.30	$59.30
Purchase #4	$148.29	3.384%	$153.3081	$153.31	$153.30	$153.30
Purchase #5	$31.50	12.715%	$35.5052	$35.51	$35.50	$35.50
Purchase #6	$122.30	6.315%	$130.0232	$130.02	$130.00	$130.00
Purchase #7	$122.77	13.187%	$138.9597	$138.96	$138.95	$139.00
7 purchase totals =	$850.49		$903.9934	$903.99	$903.90	$904.00