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	$55.78	6.367%	$59.3315	$59.33	$59.35	$59.30
Purchase #2	$123.72	7.307%	$132.7602	$132.76	$132.75	$132.80
Purchase #3	$240.41	12.157%	$269.6366	$269.64	$269.65	$269.60
Purchase #4	$38.74	4.438%	$40.4593	$40.46	$40.45	$40.50
Purchase #5	$134.57	6.410%	$143.1959	$143.20	$143.20	$143.20
Purchase #6	$224.38	13.807%	$255.3601	$255.36	$255.35	$255.40
Purchase #7	$171.85	11.800%	$192.1283	$192.13	$192.15	$192.10
7 purchase totals =	$989.45		$1,092.8719	$1,092.88	$1,092.90	$1,092.90