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	$95.59	8.571%	$103.783	$103.78	$103.80	$103.80
Purchase #2	$225.65	12.279%	$253.3576	$253.36	$253.35	$253.40
Purchase #3	$127.35	12.829%	$143.6877	$143.69	$143.70	$143.70
Purchase #4	$179.32	11.583%	$200.0906	$200.09	$200.10	$200.10
Purchase #5	$106.38	12.767%	$119.9615	$119.96	$119.95	$120.00
Purchase #6	$179.48	7.498%	$192.9374	$192.94	$192.95	$192.90
Purchase #7	$75.73	5.689%	$80.0383	$80.04	$80.05	$80.00
7 purchase totals =	$989.50		$1,093.8561	$1,093.86	$1,093.90	$1,093.90