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	$168.71	12.561%	$189.9017	$189.90	$189.90	$189.90
Purchase #2	$9.36	12.596%	$10.539	$10.54	$10.55	$10.50
Purchase #3	$78.67	6.666%	$83.9141	$83.91	$83.90	$83.90
Purchase #4	$10.88	11.399%	$12.1202	$12.12	$12.10	$12.10
Purchase #5	$131.43	10.509%	$145.242	$145.24	$145.25	$145.20
Purchase #6	$148.83	11.736%	$166.2967	$166.30	$166.30	$166.30
Purchase #7	$152.82	12.210%	$171.4793	$171.48	$171.50	$171.50
7 purchase totals =	$700.70		$779.4930	$779.49	$779.50	$779.40