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	$9.49	12.804%	$10.7051	$10.71	$10.70	$10.70
Purchase #2	$69.64	4.357%	$72.6742	$72.67	$72.65	$72.70
Purchase #3	$221.56	12.438%	$249.1176	$249.12	$249.10	$249.10
Purchase #4	$80.88	12.284%	$90.8153	$90.82	$90.80	$90.80
Purchase #5	$45.69	11.583%	$50.9823	$50.98	$51.00	$51.00
Purchase #6	$85.74	4.869%	$89.9147	$89.91	$89.90	$89.90
Purchase #7	$142.96	9.179%	$156.0823	$156.08	$156.10	$156.10
7 purchase totals =	$655.96		$720.2915	$720.29	$720.25	$720.30