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	$108.46	5.569%	$114.5001	$114.50	$114.50	$114.50
Purchase #2	$174.74	12.188%	$196.0373	$196.04	$196.05	$196.00
Purchase #3	$101.96	4.503%	$106.5513	$106.55	$106.55	$106.60
Purchase #4	$6.95	7.518%	$7.4725	$7.47	$7.45	$7.50
Purchase #5	$74.70	11.265%	$83.115	$83.12	$83.10	$83.10
Purchase #6	$181.38	12.315%	$203.7169	$203.72	$203.70	$203.70
Purchase #7	$152.70	12.721%	$172.125	$172.13	$172.15	$172.10
7 purchase totals =	$800.89		$883.5181	$883.53	$883.50	$883.50