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	$98.77	9.442%	$108.0959	$108.10	$108.10	$108.10
Purchase #2	$64.30	5.231%	$67.6635	$67.66	$67.65	$67.70
Purchase #3	$77.73	3.821%	$80.7001	$80.70	$80.70	$80.70
Purchase #4	$98.45	3.710%	$102.1025	$102.10	$102.10	$102.10
Purchase #5	$109.71	8.358%	$118.8796	$118.88	$118.90	$118.90
Purchase #6	$36.46	12.639%	$41.0682	$41.07	$41.05	$41.10
Purchase #7	$109.48	6.776%	$116.8984	$116.90	$116.90	$116.90
7 purchase totals =	$594.90		$635.4082	$635.41	$635.40	$635.50