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	$84.30	10.439%	$93.1001	$93.10	$93.10	$93.10
Purchase #2	$58.96	10.321%	$65.0453	$65.05	$65.05	$65.00
Purchase #3	$67.37	7.387%	$72.3466	$72.35	$72.35	$72.30
Purchase #4	$73.37	13.722%	$83.4378	$83.44	$83.45	$83.40
Purchase #5	$96.34	13.572%	$109.4153	$109.42	$109.40	$109.40
Purchase #6	$242.75	11.291%	$270.1589	$270.16	$270.15	$270.20
Purchase #7	$139.91	5.712%	$147.9017	$147.90	$147.90	$147.90
7 purchase totals =	$763.00		$841.4057	$841.42	$841.40	$841.30