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	$121.87	9.214%	$133.0991	$133.10	$133.10	$133.10
Purchase #2	$102.91	7.699%	$110.833	$110.83	$110.85	$110.80
Purchase #3	$190.29	3.379%	$196.7199	$196.72	$196.70	$196.70
Purchase #4	$142.89	9.490%	$156.4503	$156.45	$156.45	$156.50
Purchase #5	$135.41	9.567%	$148.3647	$148.36	$148.35	$148.40
Purchase #6	$41.26	3.527%	$42.7152	$42.72	$42.70	$42.70
Purchase #7	$172.83	9.498%	$189.2454	$189.25	$189.25	$189.20
7 purchase totals =	$907.46		$977.4276	$977.43	$977.40	$977.40