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	$222.63	3.543%	$230.5178	$230.52	$230.50	$230.50
Purchase #2	$134.37	13.697%	$152.7747	$152.77	$152.75	$152.80
Purchase #3	$207.37	9.655%	$227.3916	$227.39	$227.40	$227.40
Purchase #4	$79.25	5.804%	$83.8497	$83.85	$83.85	$83.80
Purchase #5	$5.61	5.303%	$5.9075	$5.91	$5.90	$5.90
Purchase #6	$142.64	3.280%	$147.3186	$147.32	$147.30	$147.30
Purchase #7	$40.69	3.769%	$42.2236	$42.22	$42.20	$42.20
7 purchase totals =	$832.56		$889.9835	$889.98	$889.90	$889.90