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	$123.37	3.272%	$127.4067	$127.41	$127.40	$127.40
Purchase #2	$133.28	4.372%	$139.107	$139.11	$139.10	$139.10
Purchase #3	$207.32	7.198%	$222.2429	$222.24	$222.25	$222.20
Purchase #4	$94.68	7.389%	$101.6759	$101.68	$101.70	$101.70
Purchase #5	$65.53	8.588%	$71.1577	$71.16	$71.15	$71.20
Purchase #6	$79.32	7.480%	$85.2531	$85.25	$85.25	$85.30
Purchase #7	$174.82	9.172%	$190.8545	$190.85	$190.85	$190.90
7 purchase totals =	$878.32		$937.6978	$937.70	$937.70	$937.80