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	$92.54	9.756%	$101.5682	$101.57	$101.55	$101.60
Purchase #2	$151.71	11.706%	$169.4692	$169.47	$169.45	$169.50
Purchase #3	$134.42	12.327%	$150.99	$150.99	$151.00	$151.00
Purchase #4	$83.64	6.615%	$89.1728	$89.17	$89.15	$89.20
Purchase #5	$67.63	7.536%	$72.7266	$72.73	$72.75	$72.70
Purchase #6	$40.93	10.811%	$45.3549	$45.35	$45.35	$45.40
Purchase #7	$192.67	8.292%	$208.6462	$208.65	$208.65	$208.60
7 purchase totals =	$763.54		$837.9279	$837.93	$837.90	$838.00