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	$134.98	12.824%	$152.2898	$152.29	$152.30	$152.30
Purchase #2	$167.72	10.669%	$185.614	$185.61	$185.60	$185.60
Purchase #3	$227.92	9.774%	$250.1969	$250.20	$250.20	$250.20
Purchase #4	$82.41	10.143%	$90.7688	$90.77	$90.75	$90.80
Purchase #5	$49.32	7.789%	$53.1615	$53.16	$53.15	$53.20
Purchase #6	$198.58	11.854%	$222.1197	$222.12	$222.10	$222.10
Purchase #7	$179.32	3.763%	$186.0678	$186.07	$186.05	$186.10
7 purchase totals =	$1,040.25		$1,140.2185	$1,140.22	$1,140.15	$1,140.30