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	$204.66	5.202%	$215.3064	$215.31	$215.30	$215.30
Purchase #2	$135.44	11.408%	$150.891	$150.89	$150.90	$150.90
Purchase #3	$104.88	9.508%	$114.852	$114.85	$114.85	$114.90
Purchase #4	$142.36	9.257%	$155.5383	$155.54	$155.55	$155.50
Purchase #5	$39.30	3.531%	$40.6877	$40.69	$40.70	$40.70
Purchase #6	$189.69	7.328%	$203.5905	$203.59	$203.60	$203.60
Purchase #7	$185.55	6.116%	$196.8982	$196.90	$196.90	$196.90
7 purchase totals =	$1,001.88		$1,077.7641	$1,077.77	$1,077.80	$1,077.80