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	$126.65	10.398%	$139.8191	$139.82	$139.80	$139.80
Purchase #2	$238.47	13.144%	$269.8145	$269.81	$269.80	$269.80
Purchase #3	$165.98	7.529%	$178.4766	$178.48	$178.50	$178.50
Purchase #4	$171.32	7.775%	$184.6401	$184.64	$184.65	$184.60
Purchase #5	$94.95	6.293%	$100.9252	$100.93	$100.95	$100.90
Purchase #6	$7.60	11.147%	$8.4472	$8.45	$8.45	$8.40
Purchase #7	$169.82	7.697%	$182.891	$182.89	$182.90	$182.90
7 purchase totals =	$974.79		$1,065.0137	$1,065.02	$1,065.05	$1,064.90