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	$18.69	7.868%	$20.1605	$20.16	$20.15	$20.20
Purchase #2	$88.66	12.378%	$99.6343	$99.63	$99.65	$99.60
Purchase #3	$107.83	11.358%	$120.0773	$120.08	$120.10	$120.10
Purchase #4	$119.90	9.347%	$131.1071	$131.11	$131.10	$131.10
Purchase #5	$231.50	11.470%	$258.0531	$258.05	$258.05	$258.10
Purchase #6	$126.80	11.675%	$141.6039	$141.60	$141.60	$141.60
Purchase #7	$224.70	3.839%	$233.3262	$233.33	$233.35	$233.30
7 purchase totals =	$918.08		$1,003.9624	$1,003.96	$1,004.00	$1,004.00