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	$125.40	9.568%	$137.3983	$137.40	$137.40	$137.40
Purchase #2	$42.71	11.414%	$47.5849	$47.58	$47.60	$47.60
Purchase #3	$231.80	4.244%	$241.6376	$241.64	$241.65	$241.60
Purchase #4	$203.33	6.456%	$216.457	$216.46	$216.45	$216.50
Purchase #5	$238.39	8.234%	$258.019	$258.02	$258.00	$258.00
Purchase #6	$18.65	10.427%	$20.5946	$20.59	$20.60	$20.60
Purchase #7	$73.54	9.339%	$80.4079	$80.41	$80.40	$80.40
7 purchase totals =	$933.82		$1,002.0993	$1,002.10	$1,002.10	$1,002.10