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	$150.28	10.872%	$166.6184	$166.62	$166.60	$166.60
Purchase #2	$236.33	5.561%	$249.4723	$249.47	$249.45	$249.50
Purchase #3	$30.73	6.147%	$32.619	$32.62	$32.60	$32.60
Purchase #4	$117.88	11.209%	$131.0932	$131.09	$131.10	$131.10
Purchase #5	$54.46	4.438%	$56.8769	$56.88	$56.90	$56.90
Purchase #6	$91.38	11.401%	$101.7982	$101.80	$101.80	$101.80
Purchase #7	$171.82	4.710%	$179.9127	$179.91	$179.90	$179.90
7 purchase totals =	$852.88		$918.3907	$918.39	$918.35	$918.40