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	$35.53	9.544%	$38.921	$38.92	$38.90	$38.90
Purchase #2	$41.63	13.697%	$47.3321	$47.33	$47.35	$47.30
Purchase #3	$102.54	3.162%	$105.7823	$105.78	$105.80	$105.80
Purchase #4	$225.71	6.340%	$240.02	$240.02	$240.00	$240.00
Purchase #5	$170.63	9.312%	$186.5191	$186.52	$186.50	$186.50
Purchase #6	$142.61	11.124%	$158.4739	$158.47	$158.45	$158.50
Purchase #7	$55.85	10.474%	$61.6997	$61.70	$61.70	$61.70
7 purchase totals =	$774.50		$838.7481	$838.74	$838.70	$838.70