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	$208.48	7.110%	$223.3029	$223.30	$223.30	$223.30
Purchase #2	$81.72	10.284%	$90.1241	$90.12	$90.10	$90.10
Purchase #3	$93.97	5.202%	$98.8583	$98.86	$98.85	$98.90
Purchase #4	$181.90	3.689%	$188.6103	$188.61	$188.60	$188.60
Purchase #5	$110.83	4.651%	$115.9847	$115.98	$116.00	$116.00
Purchase #6	$185.85	3.655%	$192.6428	$192.64	$192.65	$192.60
Purchase #7	$137.46	13.853%	$156.5023	$156.50	$156.50	$156.50
7 purchase totals =	$1,000.21		$1,066.0254	$1,066.01	$1,066.00	$1,066.00