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	$69.29	3.207%	$71.5121	$71.51	$71.50	$71.50
Purchase #2	$238.41	10.667%	$263.8412	$263.84	$263.85	$263.80
Purchase #3	$124.77	11.696%	$139.3631	$139.36	$139.35	$139.40
Purchase #4	$118.75	5.552%	$125.343	$125.34	$125.35	$125.30
Purchase #5	$140.52	9.467%	$153.823	$153.82	$153.80	$153.80
Purchase #6	$167.61	7.108%	$179.5237	$179.52	$179.50	$179.50
Purchase #7	$139.72	12.117%	$156.6499	$156.65	$156.65	$156.60
7 purchase totals =	$999.07		$1,090.0560	$1,090.04	$1,090.00	$1,089.90