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	$79.69	12.530%	$89.6752	$89.68	$89.70	$89.70
Purchase #2	$230.73	5.529%	$243.4871	$243.49	$243.50	$243.50
Purchase #3	$17.88	8.408%	$19.3834	$19.38	$19.40	$19.40
Purchase #4	$241.43	10.662%	$267.1713	$267.17	$267.15	$267.20
Purchase #5	$102.94	3.499%	$106.5419	$106.54	$106.55	$106.50
Purchase #6	$139.46	12.136%	$156.3849	$156.38	$156.40	$156.40
Purchase #7	$205.32	7.566%	$220.8545	$220.85	$220.85	$220.90
7 purchase totals =	$1,017.45		$1,103.4983	$1,103.49	$1,103.55	$1,103.60