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	$138.78	13.760%	$157.8761	$157.88	$157.90	$157.90
Purchase #2	$141.97	10.289%	$156.5773	$156.58	$156.60	$156.60
Purchase #3	$232.46	9.854%	$255.3666	$255.37	$255.35	$255.40
Purchase #4	$26.45	10.227%	$29.155	$29.16	$29.15	$29.20
Purchase #5	$170.72	12.143%	$191.4505	$191.45	$191.45	$191.50
Purchase #6	$128.90	12.863%	$145.4804	$145.48	$145.50	$145.50
Purchase #7	$79.41	13.571%	$90.1867	$90.19	$90.20	$90.20
7 purchase totals =	$918.69		$1,026.0926	$1,026.11	$1,026.15	$1,026.30