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	$73.90	6.634%	$78.8025	$78.80	$78.80	$78.80
Purchase #2	$144.89	7.307%	$155.4771	$155.48	$155.50	$155.50
Purchase #3	$136.72	6.759%	$145.9609	$145.96	$145.95	$146.00
Purchase #4	$213.66	9.735%	$234.4598	$234.46	$234.45	$234.50
Purchase #5	$170.74	8.590%	$185.4066	$185.41	$185.40	$185.40
Purchase #6	$129.27	7.196%	$138.5723	$138.57	$138.55	$138.60
Purchase #7	$146.70	5.560%	$154.8565	$154.86	$154.85	$154.90
7 purchase totals =	$1,015.88		$1,093.5357	$1,093.54	$1,093.50	$1,093.70