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	$90.98	9.118%	$99.2756	$99.28	$99.30	$99.30
Purchase #2	$181.46	10.839%	$201.1284	$201.13	$201.15	$201.10
Purchase #3	$110.27	7.646%	$118.7012	$118.70	$118.70	$118.70
Purchase #4	$250.25	4.623%	$261.8191	$261.82	$261.80	$261.80
Purchase #5	$144.34	12.639%	$162.5831	$162.58	$162.60	$162.60
Purchase #6	$250.46	3.611%	$259.5041	$259.50	$259.50	$259.50
Purchase #7	$189.52	5.665%	$200.2563	$200.26	$200.25	$200.30
7 purchase totals =	$1,217.28		$1,303.2678	$1,303.27	$1,303.30	$1,303.30