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	$25.60	13.812%	$29.1359	$29.14	$29.15	$29.10
Purchase #2	$46.90	4.227%	$48.8825	$48.88	$48.90	$48.90
Purchase #3	$128.72	9.450%	$140.884	$140.88	$140.90	$140.90
Purchase #4	$213.86	8.418%	$231.8627	$231.86	$231.85	$231.90
Purchase #5	$64.40	7.328%	$69.1192	$69.12	$69.10	$69.10
Purchase #6	$250.29	4.544%	$261.6632	$261.66	$261.65	$261.70
Purchase #7	$198.66	11.775%	$222.0522	$222.05	$222.05	$222.10
7 purchase totals =	$928.43		$1,003.5997	$1,003.59	$1,003.60	$1,003.70