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	$94.65	12.540%	$106.5191	$106.52	$106.50	$106.50
Purchase #2	$152.37	10.820%	$168.8564	$168.86	$168.85	$168.90
Purchase #3	$66.91	9.645%	$73.3635	$73.36	$73.35	$73.40
Purchase #4	$41.59	9.638%	$45.5984	$45.60	$45.60	$45.60
Purchase #5	$216.40	6.185%	$229.7843	$229.78	$229.80	$229.80
Purchase #6	$151.41	9.517%	$165.8197	$165.82	$165.80	$165.80
Purchase #7	$116.88	5.467%	$123.2698	$123.27	$123.25	$123.30
7 purchase totals =	$840.21		$913.2112	$913.21	$913.15	$913.30