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	$65.52	3.549%	$67.8453	$67.85	$67.85	$67.80
Purchase #2	$138.83	6.213%	$147.4555	$147.46	$147.45	$147.50
Purchase #3	$134.47	5.472%	$141.8282	$141.83	$141.85	$141.80
Purchase #4	$92.43	12.741%	$104.2065	$104.21	$104.20	$104.20
Purchase #5	$40.66	12.850%	$45.8848	$45.88	$45.90	$45.90
Purchase #6	$60.64	12.523%	$68.2339	$68.23	$68.25	$68.20
Purchase #7	$70.78	6.409%	$75.3163	$75.32	$75.30	$75.30
7 purchase totals =	$603.33		$650.7705	$650.78	$650.80	$650.70