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	$59.46	9.152%	$64.9018	$64.90	$64.90	$64.90
Purchase #2	$166.83	10.842%	$184.9177	$184.92	$184.90	$184.90
Purchase #3	$219.91	11.689%	$245.6153	$245.62	$245.60	$245.60
Purchase #4	$150.86	6.828%	$161.1607	$161.16	$161.15	$161.20
Purchase #5	$144.52	9.260%	$157.9026	$157.90	$157.90	$157.90
Purchase #6	$119.39	10.387%	$131.791	$131.79	$131.80	$131.80
Purchase #7	$124.39	12.627%	$140.0967	$140.10	$140.10	$140.10
7 purchase totals =	$985.36		$1,086.3858	$1,086.39	$1,086.35	$1,086.40