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	$83.31	10.688%	$92.2142	$92.21	$92.20	$92.20
Purchase #2	$36.97	8.295%	$40.0367	$40.04	$40.05	$40.00
Purchase #3	$140.82	13.459%	$159.773	$159.77	$159.75	$159.80
Purchase #4	$84.50	7.556%	$90.8848	$90.88	$90.90	$90.90
Purchase #5	$234.42	10.622%	$259.3201	$259.32	$259.30	$259.30
Purchase #6	$94.61	6.661%	$100.912	$100.91	$100.90	$100.90
Purchase #7	$229.27	13.554%	$260.3453	$260.35	$260.35	$260.30
7 purchase totals =	$903.90		$1,003.4861	$1,003.48	$1,003.45	$1,003.40