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	$44.94	11.107%	$49.9315	$49.93	$49.95	$49.90
Purchase #2	$215.32	3.387%	$222.6129	$222.61	$222.60	$222.60
Purchase #3	$220.88	13.864%	$251.5028	$251.50	$251.50	$251.50
Purchase #4	$154.63	8.552%	$167.854	$167.85	$167.85	$167.90
Purchase #5	$53.40	12.681%	$60.1717	$60.17	$60.15	$60.20
Purchase #6	$139.88	7.529%	$150.4116	$150.41	$150.40	$150.40
Purchase #7	$103.27	3.555%	$106.9412	$106.94	$106.95	$106.90
7 purchase totals =	$932.32		$1,009.4257	$1,009.41	$1,009.40	$1,009.40