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	$130.93	6.256%	$139.121	$139.12	$139.10	$139.10
Purchase #2	$120.50	6.693%	$128.5651	$128.57	$128.55	$128.60
Purchase #3	$56.52	8.537%	$61.3451	$61.35	$61.35	$61.30
Purchase #4	$137.29	7.102%	$147.0403	$147.04	$147.05	$147.00
Purchase #5	$67.98	7.614%	$73.156	$73.16	$73.15	$73.20
Purchase #6	$128.85	10.634%	$142.5519	$142.55	$142.55	$142.60
Purchase #7	$226.42	5.161%	$238.1055	$238.11	$238.10	$238.10
7 purchase totals =	$868.49		$929.8849	$929.90	$929.85	$929.90