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	$167.28	4.224%	$174.3459	$174.35	$174.35	$174.30
Purchase #2	$202.36	11.145%	$224.913	$224.91	$224.90	$224.90
Purchase #3	$230.75	7.583%	$248.2478	$248.25	$248.25	$248.20
Purchase #4	$103.77	9.758%	$113.8959	$113.90	$113.90	$113.90
Purchase #5	$227.38	10.119%	$250.3886	$250.39	$250.40	$250.40
Purchase #6	$241.37	3.668%	$250.2235	$250.22	$250.20	$250.20
Purchase #7	$48.40	10.614%	$53.5372	$53.54	$53.55	$53.50
7 purchase totals =	$1,221.31		$1,315.5519	$1,315.56	$1,315.55	$1,315.40