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	$156.77	8.654%	$170.3369	$170.34	$170.35	$170.30
Purchase #2	$199.93	13.465%	$226.8506	$226.85	$226.85	$226.90
Purchase #3	$236.34	11.213%	$262.8408	$262.84	$262.85	$262.80
Purchase #4	$208.78	7.259%	$223.9353	$223.94	$223.95	$223.90
Purchase #5	$162.78	4.371%	$169.8951	$169.90	$169.90	$169.90
Purchase #6	$23.83	10.194%	$26.2592	$26.26	$26.25	$26.30
Purchase #7	$28.45	10.276%	$31.3735	$31.37	$31.35	$31.40
7 purchase totals =	$1,016.88		$1,111.4914	$1,111.50	$1,111.50	$1,111.50