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	$107.51	11.114%	$119.4587	$119.46	$119.45	$119.50
Purchase #2	$165.75	7.870%	$178.7945	$178.79	$178.80	$178.80
Purchase #3	$29.61	9.322%	$32.3702	$32.37	$32.35	$32.40
Purchase #4	$83.68	6.444%	$89.0723	$89.07	$89.05	$89.10
Purchase #5	$41.89	13.266%	$47.4471	$47.45	$47.45	$47.40
Purchase #6	$136.59	5.364%	$143.9167	$143.92	$143.90	$143.90
Purchase #7	$246.51	8.755%	$268.092	$268.09	$268.10	$268.10
7 purchase totals =	$811.54		$879.1515	$879.15	$879.10	$879.20