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	$8.51	6.745%	$9.084	$9.08	$9.10	$9.10
Purchase #2	$78.41	9.726%	$86.0362	$86.04	$86.05	$86.00
Purchase #3	$156.35	12.618%	$176.0782	$176.08	$176.10	$176.10
Purchase #4	$175.96	5.265%	$185.2243	$185.22	$185.20	$185.20
Purchase #5	$239.94	9.512%	$262.7631	$262.76	$262.75	$262.80
Purchase #6	$130.87	7.823%	$141.108	$141.11	$141.10	$141.10
Purchase #7	$147.85	5.836%	$156.4785	$156.48	$156.50	$156.50
7 purchase totals =	$937.89		$1,016.7723	$1,016.77	$1,016.80	$1,016.80