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	$33.47	5.205%	$35.2121	$35.21	$35.20	$35.20
Purchase #2	$65.59	3.337%	$67.7787	$67.78	$67.80	$67.80
Purchase #3	$177.63	6.745%	$189.6111	$189.61	$189.60	$189.60
Purchase #4	$233.63	10.601%	$258.3971	$258.40	$258.40	$258.40
Purchase #5	$100.35	6.230%	$106.6018	$106.60	$106.60	$106.60
Purchase #6	$205.30	11.496%	$228.9013	$228.90	$228.90	$228.90
Purchase #7	$191.63	8.705%	$208.3114	$208.31	$208.30	$208.30
7 purchase totals =	$1,007.60		$1,094.8135	$1,094.81	$1,094.80	$1,094.80