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	$230.46	3.661%	$238.8971	$238.90	$238.90	$238.90
Purchase #2	$244.45	10.747%	$270.721	$270.72	$270.70	$270.70
Purchase #3	$103.29	7.584%	$111.1235	$111.12	$111.10	$111.10
Purchase #4	$7.59	10.453%	$8.3834	$8.38	$8.40	$8.40
Purchase #5	$26.51	3.705%	$27.4922	$27.49	$27.50	$27.50
Purchase #6	$185.56	11.180%	$206.3056	$206.31	$206.30	$206.30
Purchase #7	$152.83	9.372%	$167.1532	$167.15	$167.15	$167.20
7 purchase totals =	$950.69		$1,030.0760	$1,030.07	$1,030.05	$1,030.10